Europe's travel chaos is easing slightly as airports recover following a winter storm, but travellers are warned they could still face delays and cancellations as airlines struggle to clear the backlog.

Officials at London's Heathrow Airport said they expect roughly 70 per cent of the planned departures — about 900 flights — will operate Wednesday.

The busy international hub has struggled to get planes in the air since about 13 centimetres of snow fell on Saturday.

Crews struggled to clear snow and de-ice equipment after the storm, creating widespread delays. The second runway wasn't cleared until Tuesday, leaving thousands of people stranded during the busy holiday travel season.

Crowds at Heathrow were smaller Wednesday, with fewer people in lineups outside the terminals or sleeping on the floors, but airports cautioned travellers to expect continued delays in the days ahead.

"Planes and crews are in the wrong place all over the world because they weren't able to land at Heathrow for a few days," CBC's Ann MacMillan said from London.

Heathrow gave Air Canada permission to resume its full schedule of flights heading to London, beginning Tuesday evening, after turning away aircraft because of snow-clogged runways.

But Air Canada said it may take more than a week to move all passengers who were booked to travel to and from London, "due to capacity restrictions at Heathrow," and because its aircraft were already heavily booked prior to the holiday season.

Travellers sleep on camp beds provided by airport operator Fraport at Frankfurt Airport on Wednesday. (Kai Pfaffenbach/Reuters)

The European Commission has criticized the travel disruptions and told airports they must get serious about planning for winter weather. Meanwhile, frustrated passengers can only wait and wonder how the situation got so bad.

"What I don't understand it's like, in Vienna if it snows like that, there's no problem at all. The planes are taking off," said Jotte Koenig, a traveller from Austria.

Colin Matthews, chief executive of airport operator BAA, said Wednesday he has decided to give up his bonus and his focus is on "keeping people moving and rebuilding confidence in Heathrow."

Germany's Frankfurt Airport said schedules were slowly returning to normal after several days of widespread delays caused by winter weather. About 70 flights were cancelled Wednesday from a daily total of about 1,300, compared to the 550 cancellations on Tuesday.

The French government said 15 per cent of the flights from Charles de Gaulle airport in Paris would be cancelled Wednesday.

Travellers are still being advised to contact their airlines before heading to Heathrow, Frankfurt or other affected European airports.

Eurostar said train services between Britain and continental Europe were operating a near-normal schedule, but asked that only customers with tickets show up at terminals after thousands lined up to purchase them earlier this week.

"Although the U.K. is seeing a break from fresh snow, temperatures remain frigid for the next few days. With afternoon highs only just above zero, de-icing will need to continue," CBC meteorologist Johanna Wagstaffe said.

Wagstaffe said the next storm will move in for Christmas Day into Boxing Day.

"This storm will actually be breaking off from our nor'easter hitting the Maritimes right now, and crossing the Atlantic," she said.

With files from the Associated Press