The millions of people stranded by widespread flight shutdowns across Europe had reason for hope Monday as officials announced a plan to partially re-open the skies to air traffic.

"From tomorrow morning on we should see progressively more planes start to fly," European Transport Commissioner Siim Kallas told reporters. "And this is good news for Europe's stranded passengers, good news for airline industry and other sectors hard hit by this crisis."

There will be limits, as the ash coming from Iceland's Eyjafjallajokull volcano continues to present problems. Tuesday's re-opening will not bring air traffic to its usual levels. European Union officials agreed to a plan involving three zones - one that remains closed, one open to all flights and one only open to certain flights.

The new measures will go into effect Tuesday morning, Kallas said.

There will not be "any compromise on safety," Kallas said. He called the current situation "unsustainable," and said it is clear "we cannot just wait until this ash cloud dissipates."

Kallas rejected suggestions that European Union ministers should have acted more quickly to allow flights to resume. It took Sunday's test flights to provide the information necessary, he said.

Since the volcanic eruption worsened last week, sending an ash cloud into the skies, airlines have been losing at least $200 million a day, according to the International Air Transport Association, the trade group representing airlines. Airports had lost close to 136 million euros ($184 million) as of Sunday, said Olivier Jankovec, director general of Airports Council International, Europe.

More than 6.8 million passengers have been affected, Jankovec said in a statement, adding that the effect is worse than after the September 11, 2001, terror attacks on the United States.