Heathrow Airport has warned access to Terminals 2 and 3 is restricted because of flooding.
Water in the central terminal area means anyone trying to travel to or from either of these terminals cannot travel by road.
Instead passengers are being advised to travel by rail and tube and to avoid using cars.
"Our teams are working to resolve the situation as quickly as possible, we apologise for any disruption caused," the airport said early on Saturday.
The disruption comes during the school holidays, one of the busiest periods for the airport.
Heathrow said 19 July was its busiest day of the year so far as many schools broke up for summer, with 267,000 passengers passing through.
The airport was recently affected by disruption to railway services, after a water leak prompted the closure of a tunnel.
Get in touch
Have you been affected by the issues in this story? Share your experiences
This breaking news story is being updated and more details will be published shortly. Please refresh the page for the fullest version.
You can receive Breaking News on a smartphone or tablet via the BBC News App. You can also follow @BBCBreaking on X to get the latest alerts.