A fire at an electrical substation near London’s Heathrow Airport has closed one of the world’s busiest airports.

Heathrow Airport said the fire at the substation, which supplies power to the airport, has caused a “significant power outage” and the airport is expected to be closed until 11:59 p.m. local time on Friday night.

British Airways, which has a hub at Heathrow Airport, said it is advising travelers not to go to the airport and that they are working to notify passengers of their travel options for the next 24 hours and beyond as soon as possible.

Meanwhile, inbound flights to Heathrow are being redirected to other U.K. airports, officials said.

“Due to a power outage in the London Heathrow area, London Heathrow Airport is currently closed,” British Airways said. “As a result, customers due to travel from Heathrow on Friday are advised not to travel to the airport until further notice. This will clearly have a significant impact on our operation and our customers and we’re working as quickly as possible to update them on their travel options for the next 24 hours and beyond.”

The fire has caused a power outage affecting a large numbers of homes and businesses and led to some evacuations, the fire brigade said. Firefighters led 29 people to safety from neighboring properties and, as a precaution, established a cordon around the area and evacuated about 150 people.

“This is a highly visible and significant incident, and our firefighters are working tirelessly in challenging conditions to bring the fire under control as swiftly as possible,” Pat Goulbourne, assistant commissioner of the London Fire Brigade, said in a statement shortly before 2 a.m. local time.

The cause of the fire is not yet known, the fire brigade said.

This is a developing story. Please check back for updates.