Europe's air traffic slowly returned to normal Tuesday with almost half of scheduled flights taking to the skies, but officials warn it could take weeks to clear the backlog of millions of passengers stranded after an Icelandic volcano erupted on April 14.

The British authority reopens its airspace from 10:00 p.m. on Tuesday, and a plane of British Airways has landed in the Heathrow Airport in London just around that time.[Xinhua]

After the EU allowed member states to open their airspace early on Tuesday, Britain reopened air traffic at night after some delays, joining the Netherlands, France, Germany and other countries who already allowed some airlines to fly since Monday.

Eurocontrol, the body coordinating air traffic control across the region, said almost three-quarters of European airspace were open late Tuesday. It expected just under half of the 27,500 flights over Europe to take off, a marked improvement over the last few days.

Eurocontrol predicted the number of takeoffs to be almost back to normal by Friday.

At London's Heathrow airport, Europe's busiest, a British Airways flight from Vancouver touched down Tuesday night, the first flight since the shutdown, signaling the opening of British airspace and giving a huge boost to travelers and air freight.

British Airways said it expected about two dozen flights from the United States, Africa and Asia to land by early Wednesday.

The Netherlands led the continent in allowing passenger flights Monday. Air France plans to run all long-haul flights on Wednesday, while Poland announced it would reopen its airspace Wednesday morning as of 0500 GMT.

Germany, with its major Frankfurt hub, kept its airspace largely closed until at least 0000GMT, although some 800 flights operated on Tuesday.