Around 50 percent of flights scheduled in Europe for Tuesday are expected to take place, the European Organization for the Safety of Air Navigation, or Eurocontrol, said.

The body said in a statement that it "expected 14,000 flights to take place today in European airspace, representing half of scheduled air traffic."

"On a normal Tuesday, we would expect between 27,000 and 28,000. By the end of today, we expect that more than 95,000 flights in total will have been canceled since April 15," it said.

On Monday, EU transport ministers agreed to gradually lift flight restrictions from 0600 GMT on Tuesday, which have been imposed since an volcano in Iceland started spewing ash last week.

Under the agreement, European airspace is divided into three zones. The first zone with high density of the volcanic ash, or the no-fly zone, is not open to any flight. The second zone with lower density is left to national air traffic authorities to decide whether to open it to flights. The third zone covers airspace that is not affected by the volcanic ash.

The volcano under the Eyjafjallajokull glacier in southeast Iceland began erupting on April 14 for the second time in a month, hurling a plume of ash 6 to 11 km into the atmosphere and causing the biggest travel chaos in years in Europe.

Volcanic ash contains tiny particles of glass and pulverized rock that can damage engines and airframes. So far, tens of thousands of flights have been grounded due to the volcanic ash cloud, causing billions of euros in loss.