Dense fog caused cancellations, delays and diversions at Heathrow on Wednesday morning.
Some incoming flights were diverted to different airports, while passengers faced delays of at least an hour and more flights were cancelled into the afternoon.
According to reports, two flights from the US were diverted to land at Birmingham International, as were some British Airways flights. Flights have also been diverted to Bournemouth and Cardiff airports.
It is believed the cause of the diversion is thick fog over Heathrow, with visibility down to 200m.
Departures are also affected and Heathrow has advised travellers to contact their airline before flying.
According to flight tracker NaveX Systems, almost 20 flights have been cancelled today.
British Airways said: "We’re aiming to rebook passengers automatically.
"If your booking hasn’t been updated yet please make your way to a Customer Service desk so our airport team can assist you."
The airline added: "When there’s bad weather, we have to reduce the amount of flights that can depart and arrive into the airport."
There were also reports of traffic congestion near the airport on Wednesday morning.
