Disruption grew through the day at London's Heathrow, Gatwick and Stansted airports, as well as at Manchester and Belfast, according to Flightradar24, which tracks plane movements in real-time.

Hundreds of flights were delayed into and out of Heathrow -- the country's busiest hub -- and Gatwick, while both each saw more than a dozen departures cancelled, the site reported.

More than half of Heathrow's departing flights were showing as delayed, according to Flightradar24.

The same airports also saw disruption on Friday due to the foggy conditions.

"As widespread fog continues to affect some UK airports today, temporary air traffic restrictions remain in place at locations with low visibility," the air traffic control authority NATS said.

It said the restrictions were to maintain safety and that its teams were working closely with the airports and airlines to minimise disruption.

In some areas, thick fog patches could reduce visibility down to just 100 metres (328 feet), Britain's weather agency, the Met Office, said.

A spokesperson for Gatwick airport had earlier said the temporary air traffic restrictions in place due to fog causing poor visibility could lead to delays "throughout the day".

The disruption comes at one of the busiest times of the year for air travel.