[Updated 10:55 a.m.] CNN affiliate WMC-TV said the helicopter that crashed was operated by Hospital Wing, an organization that identifies itself on its Web site as the Memphis Medical Center's air ambulance service.
Hospital Wing said in a statement, reported by WMC-TV, that the crash occurred just east of Brownsville, and that three crew members and no patients were on board. The National Transportation Safety Board and the FAA are investigating, the statement said.
"Nothing like this has ever happened in our history," Allen Burnette, Hospital Wing's director and chief operating officer, said in the statement.
[Updated at 10:05 a.m.] A helicopter had dropped off a patient in Jackson, Tennessee, and was returning to Brownsville, Tennessee, when a crash was reported about 7:12 a.m. (8:12 a.m. ET), said FAA spokesman Lynn Lunsford.
Three people were initially reported to be on board the helicopter, Lunsford said. All three were believed to be fatalities, as the aircraft - a Eurocopter AS350 - was burned, he said.
Investigators were en route to the scene of the crash - a field near Brownsville, Lunsford said.
Asked if weather was a factor in the crash, Lunsford said, "obviously, they are going to look at everything." A weather report said there were thunderstorms in the area, but that they had passed by about 7 a.m., he said.
"The big weather system moving through had stopped a few moments before."
Officials believe the helicopter was operating under a Visual Flight Rules plan and not communicating with air traffic controllers, he said.
Visual Flight Rules, or VFR, mean a flight is conducted under visual conditions.
Asked who decides whether the weather is clear enough for a pilot to fly using VFR, Lunsford said, "There are operating guidelines in any aviation operation, but ultimately the pilot is responsible for [the] safety of [the] aircraft and deciding whether to go forward or not."
- CNN's Carolina Sanchez contributed to this report.
[Posted at 10:05 a.m.] Three people died Thursday when a medical helicopter crashed in Tennessee, the Federal Aviation Administration said.