Flooding emerged as a major concern Monday for states hit by Irene, which hit the East Coast as a hurricane and then a tropical storm over three days.

Even as Irene weakened to a tropical storm, authorities warned that its impact was not waning, especially in Vermont.

"Many Americans are still at serious risk of power outages and flooding, which could get worse in coming days as rivers swell past their banks," President Barack Obama said Sunday, adding: "The recovery effort will last for weeks or longer."

Officials said the storm had knocked out power to more than 4 million people and was responsible for at least 27 deaths.

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[Updated at 10:20 p.m.] Personnel in a state police helicopter on Monday rescued 21 people who had been stranded by post-Irene floodwaters in a Prattsville, New York, house, a local official said.

The group was stranded at a house that was cut off when all the bridges near it were washed out after torrential rains flooded homes and businesses and left the Catskill Mountains town of Prattsville largely cut off from the outside world.

Emergency workers rescued 87 people from the Prattsville area a day earlier, including 25 people who were stranded at a motel for hours after 70 mph wind gusts grounded aircraft.

[Updated at 7:32 p.m.] Vermont's governor warns that further flooding and loss of life related to Irene are likely for his state. Although small brooks have crested, large rivers have not, he said.

"It's just devastating," Gov. Peter Shumlin said. "Whole communities under water, businesses, homes, obviously roads and bridges, rail transportation infrastructure. We've lost farmers' crops," he said. "We're tough folks up here but Irene ... really hit us hard."

Three people are reported to have died in Vermont as a result of the storm. The nation's death toll from Irene is at 27.

[Updated at 5:53 p.m.] The U.S. death toll from Hurricane Irene has risen to 27, according to emergency officials.

The latest deaths were reported in Vermont. A female was killed in the Deerfield River in Wilmington, while a male was killed in Mendon after being swept away by floodwaters, according to Vermont Emergency Management. A male was found dead in Lake Rescue in Ludlow earlier Monday, authorities said.

[Updated at 5:09 p.m.] The Federal Disaster Relief Fund, the pot of money used to help communities and individuals hit by disasters, is nearly depleted. That's bad news for victims of both Hurricane Irene and other disasters like the tornadoes that hit earlier this year, CNNMoney's Chris Isidore reports.

Federal Emergency Management Agency Administrator Craig Fugate said Monday that the agency's fund has fallen to less than $800 million. With less than $1 billion on hand, the agency is only authorized to pay for emergency repairs. That means that long-term projects, like rebuilding roads, schools and other damaged structures in the tornado-ravaged southeastern states and Joplin, Mo., will have to wait.

[Updated at 3:08 p.m.] The death toll from Hurricane Irene has risen to 25, according to emergency officials.

A 64-year-old woman was found dead Sunday by Whitemarsh, Pennsylvania, police after her family grew concerned when she did not show up for work. Her body was found a half-mile from where her car was abandoned in a deluged creek, police said.

[Updated at 2:42 p.m. ET] About 5 million customers were without power Monday afternoon after Hurricane Irene passed, FEMA Administrator Crag Fugate said, citing figures from the Department of Energy.  That was down from more than 6 million, he said.

[Updated at 1:52 p.m. ET] "I can say with confidence that there's further loss of life," following flooding from Tropical Storm Irene, Vermont Gov. Peter Shumlin said Monday.

[Updated at 12:41 p.m. ET] The death toll from Hurricane Irene has risen to 24, according to police officials in New York and New Jersey.

One man in Croton, New York, died Sunday while boating along with four others down the Croton River, said Lt. Russell Haper, a spokesman for the Croton police. The boat overturned in the strong rapids. The 53-year-old man was found dead after a three-hour rescue effort. The other men were pulled safely from the water.

A 47-year-old Orange, New Jersey, man died after leaving his submerged car to wade through floodwaters to reach the post office where he worked, Kearny police said. His co-workers said that just before he would have entered the building, the man stepped into a concealed drainage creek and disappeared. Despite a two-hour rescue effort, the man's body was found about 100 yards from his car.

[Updated at 12:04 p.m. ET] The death toll from Hurricane Irene has risen to 22, according to emergency officials.

A man in Bristol, Connecticut, was killed when the canoe he and another man were riding in failed to clear a bridge on the Pequabuck River and flipped, Bristol Police Department spokesman Edward Spyros said. The man's death appeared to be an accidental drowning. The other man surfaced alive.

North Carolina has the most fatalities, six. Virginia and Pennsylvania have four each. New York and Connecticut both have two deaths, and Maryland, New Jersey, Florida and Vermont have each reported one death.

[Updated at 11:37 a.m.] About 225,000 customers were without power across Pennsylvania on Monday, according to Cathy Engel, a spokeswoman for PECO, which serves the Greater Philadelphia region. The numbers were down from a total of almost 500,000, she said.

[Updated at 10:56 a.m. ET] AirTran Airways will resume flights to New York and Boston on Monday. The airline resumed operations at Washington-area airports and all other affected airports Sunday.

AirTran expects to be operating a full schedule by Tuesday and has added some extra flights to accommodate passengers and reposition aircraft within the system.

[Updated at 10:37 a.m. ET] United and Continental flights will resume Monday from the three major New York-area airports where operations were suspended Saturday and Sunday.

The carriers also will resume service at airports in White Plains, New York; Boston; Hartford, Connecticut; Providence, Rhode Island; Portland, Maine; Manchester, New Hampshire; and Albany, New York, following Sunday flight suspensions.

[Updated at 10:11 a.m. ET] More than 8,500 people awoke Monday morning in Red Cross shelters up and down the East Coast, a spokesman for the nonprofit said.

[Updated at 10:08 a.m. ET] Dominion Power reported more than 600,000 customers were without power in Virginia and northern North Carolina.

[Updated at 10:04 a.m. ET] "Hurricane Irene's damage is likely to be characterized more by the amount of inland flooding, storm surge and treefall than by direct wind damage, and flooding is still an ongoing concern for many states in the Northeast," said Risk Management Solutions Inc., which tracks natural catastrophes.

[Updated at 9:09 a.m. ET] President Barack Obama signed an emergency declaration for the state of Vermont on Monday in the aftermath of the worst flooding in that state since 1927.

[Updated at 9:05 a.m. ET] In Pompton Lakes, New Jersey, firefighters - blocked by floodwaters - were unable to reach a house that caught fire; it burned to the ground.

[Updated at 8:57 a.m. ET] Quick update on those power-outage numbers we reported at 6:25 a.m.: The outages weren't restricted to the Northeast; they were all along Irene's path up the East Coast.

So that's about 3 million total power outages related to Irene. North Carolina alone had more than 340,000 customers without power Monday. The state emergency management agency reported the number was about 100,000 fewer than reported Sunday night.

[Updated at 8:42 a.m. ET] US Airways will resume flight operations Monday morning in the Northeast and will be back to a full schedule by Tuesday, said spokesman Todd Lehmacher. No additional flights have been added.

[Updated at 8:27 a.m. ET] As of early Monday, several states had experienced rainfall in the double digits, according to numbers from the National Weather Service. Topping the list was Bunyan, North Carolina, with 15.66 inches.

Some of the other top rainfall totals include: Burlington and East Hartford, Connecticut, which both had more than 8 inches; Ellendale and Adamsville, Delaware, which had at least 10 inches each; Savoy, Massachusetts, with more than 9 inches; the Maryland cities of Plum Point (12.96 inches), Easton (11.34) and Hickman (10.5); New Bern, Williamston, Washington and Greenville, North Carolina, which all recorded more than a foot of rain; Stockton and Wayne, New Jersey, which both saw more than 10 inches of wet stuff; Tuxedo Park, New York, which had almost a foot; and Suffolk and Newland, Virginia, which both had about 11 inches.

[Updated at 8:07 a.m. ET] As life along the East Coast began returning to normalcy Monday morning, New York announced subway service had resumed. Amtrak, meanwhile, had some service in the Northeast, but much was canceled.

[Updated at 7:49 a.m. ET] The body of a young woman washed away as she stood near a river in Wilmington, Vermont, was recovered Monday, marking the 21st death related to Hurricane Irene. The death toll spans nine states.

Vermont's flooding, some of the worst since 1927, has turned brooks into rivers and ripped homes from their foundations.

In all, 260 roads were affected, many of them underwater, Vermont's Emergency Management Department said. Four to six covered bridges were destroyed and others were washed out, it said.

In Montpelier, the capital, water crested overnight at 19.5 feet, just shy of the 20-foot prediction, but levels throughout the state were receding Monday morning. The emergency management headquarters flooded overnight and was evacuated and relocated from Waterbury to Burlington, approximately 20 miles away.

[Updated 6:55 a.m. ET] Delta Airlines said its flights into and out of New York and Newark, New Jersey, will resume around noon Monday. The airline is undecided on adding new flights to make up for the weekend's canceled flights, but spokesman Morgan Durrant said Delta expects every customer to be accommodated in the next few days.

[Updated 6:25 a.m. Monday] Power companies in the Northeast reported almost 3 million outages Monday morning after Irene tore across the region.

[Update 5:41 a.m. Monday] As many as 200 residents were isolated without power Monday on Ocracoke Island, North Carolina, near where Irene first made landfall as a hurricane on Saturday. Supply transport to Ocracoke is hampered as large chunks of a key roadway were taken out by violent ocean waves.

Sand dunes at the north end of Ocracoke "have apparently been spread across the road, so no one yet knows how badly the pavement is damaged," said Clayton Gaskill, manager of Ocracoke's tiny FM radio station WOVV.

[Update 5:29 a.m. Monday] John F. Kennedy International Airport in New York and Newark Liberty International Airport in New Jersey will reopen to incoming flights at 6 a.m. Monday, the Port Authority of New York and New Jersey said on its website. Departures from both airports are to resume at noon. LaGuardia Airport in New York will resume arrivals and departures at 7 a.m.

Read the full travel update.

[Update 5:22 a.m. Monday] The remnants of Irene knocked out power to more than 180,000 customers in Quebec, Canada, CNN affiliate CTV reports. Most of the outages were in the Montreal area, where winds hit 55 mph.

[Update 5:09 a.m. Monday] A flash-flood watch was in place in Vermont through Monday morning after 4 to 6 inches of rain fell across the state, the National Weather Service said.

[Update 3:59 a.m. Monday]  More flooding is predicted in New Jersey as rivers crest.

[Update 2:51 a.m. Monday] The city manager in Montpelier, Vermont, said he does not expect conditions to worsen in the city.

"There does not appear to be much additional flooding from what has been previously reported. Water will slowly begin receding into the morning," William J. Fraser said in a statement early Monday.

On Sunday night, Fraser had said "conditions continue to worsen dramatically" and mentioned the possibility of "major flooding" in downtown Montpelier.

[Update 2:28 a.m. Monday] Seven families who thought they had escaped the wrath of Irene are now stranded in the New York's Catskill Mountains after bridges crumbled all around them.

The 23 people - including two pregnant women, seven toddlers and three infants - are now stuck with no electricity, a dwindling supply of food and were down to one gallon of water late Sunday night.

"When we heard news about (bad weather) hitting Brooklyn, we thought we had saved ourselves," said Irina Noveck, one of those trapped at a vacation house in Prattsville, New York.

But after four bridges leading to the house collapsed, the families found themselves in a more dire predicament.

New York Gov. Andrew Cuomo's office said early Monday that emergency officials are monitoring the situation and "expect to rescue the people by sometime Monday."

[Update 12:22 a.m. Monday] Emergency officials said at least 21 people across the United States have died as a result of Hurricane Irene .

[Update 11:09 p.m. Sunday] The body of woman who apparently drowned after either falling or being swept into a storm swollen creek was recovered Sunday near New Scotland, New York State Police said. The woman's body was pulled from Onesquethaw Creek about 4:30 p.m., police said. The identity of the woman was not immediately released, though police said that a New Scotland man reported his wife missing about noon. She was last seen near the creek.

[Update 11:08 p.m. Sunday] Irene ceased being a tropical storm late Sunday as it swirled near the U.S.-Canadian border, the National Hurricane Center reported.  Despite losing its tropical characteristics, the storm continued to kick out sustained winds of 50 mph about 50 miles north of Berlin, New Hampshire.

[Update 8:41 p.m. Sunday] More details about flooding concerns in Vermont's capital, Montpelier: Jill Remick, from the state's emergency management division, said water in the area - where multiple rivers converge - could rise as high as 20 feet, above the 17.5 feet that led to substantial flooding in May in Montpelier.

See how other states are faring in this state-by-state list of Irene developments.

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