Due to a fire at an electrical substation supplying the airport, Heathrow is experiencing a significant power outage.
The fire at the substation in Hayes, in west London, has left thousands of homes without power and caused around 150 people to be evacuated from surrounding properties
The Airport will be closed until 23h59 on 21 March.
Passengers are advised not to travel to the airport and should contact their airline for further information.
“We’re working as quickly as possible to update them on their travel options for the next 24 hours and beyond,” it said in a statement.
London Gatwick Airport said “Flights are operating from London Gatwick as normal today. It accepted seven diverted flights originally scheduled to land at Heathrow”.
Long haul flights are returning to their origin Airport or diverting to Amsterdam, Frankfurt, Paris.
The airport, which serves major airlines such as British Airways and Virgin Atlantic, typically handles over 1,300 flights and 200,000 passengers daily.
