LONDON (AFP) - An unusually large blanket of thick fog descended on European airports Monday, causing scores of flight cancellations from London Heathrow, the continent's busiest, and delays at key hubs including Amsterdam and Frankfurt.

Eurocontrol, the European air traffic control organisation, said the opaque vapour also caused delays in Paris, Stuttgart, Hamburg, Berlin, Luxembourg and Brussels, though Britain was the worst affected.

"It's unusual that you have fog affecting so many airports over a couple of days," a Eurocontrol spokesman told AFP.

"We're seeing exceptionally high delay figures." The fog reduced visibility at Heathrow to less than 100 metres, Britain's Met Office said, while Eurocontrol said visibility in the Belgian capital also dropped to 100 metres.

Heathrow said around 45 flights had been cancelled, 10 per cent of the total, while London City, Manchester, Leeds Bradford, Glasgow, Belfast and Cardiff airports all reported delays.

Eurocontrol added there were a total of 122,000 minutes of flight delays across Europe due to bad weather and it is possible a number of the flights were not only delayed but actually cancelled.

Weather had improved at some airports but was getting worse again at Luxembourg, for example, he said.

A spokeswoman at Heathrow said "we've got extra passenger ambassadors in the terminals to provide assistance for those travelling today".

Heathrow officials met airlines and air navigation firm NATS to draw up a new schedule, and to decide which flights to cancel, said an airport spokeswoman.

In foggy conditions, airports have to switch to radar and "low visibility procedures" to ensure aircraft can taxi, take-off and land safely.

This increases spacing between aircraft by up to 50 per cent as they have to taxi far enough away from the runway so that their instruments do not interfere with other planes.

Budget airline Easyjet warned it was suffering "major network disruption today due to poor weather conditions throughout Europe causing low visibility".

"This has resulted in a large number of aircraft and crew out of place for flights today," it said in a statement.

Britain has been enjoying an unusually mild autumn, with temperatures hitting 22 degrees celsius on Sunday, a November record.

A driver died and a five-year-old girl was injured Sunday when a car apparently hit a tree in thick fog in Uttoxeter, central England.