LONDON — Freezing fog is causing flight delays and cancellations at Heathrow, Gatwick and London City Airport.

Fog has been an issue for London’s airports off and on for the past several days, disrupting flight schedules during one of the busiest times of the year. This latest round of foggy conditions is now in its third day.

A notice on Heathrow’s website advises passengers to check the status of their flight with their airline before travelling to the airport.