London’s Heathrow Airport announced it will be closed Friday after experiencing a “significant power outage” due to a fire. 

“Due to a fire at an electrical substation supplying the airport, Heathrow is experiencing a significant power outage,” Heathrow Airport said in a post on X, saying that “passengers are advised not to travel to the airport.” 

It was unclear exactly how many flights were immediately impacted. The airport said it would be closed through midnight Friday local time.  

The London Fire Brigade said 10 fire engines and around 70 firefighters are tackling a fire at an electrical substation in the west London town of Hayes near the airport. The cause of the fire is unknown at this time.

“The fire has caused a power outage affecting a large number of homes and local businesses, and we are working closely with our partners to minimise disruption,” Assistant Commissioner Pat Goulbourne said in a statement in which he described the fire as a “highly visible and significant incident.”

Goulbourne said firefighters had led 29 people to safety from nearby properties, and around 150 people evacuated.

Britain’s busiest airport advised travelers to contact their airline for further information.

This is a developing story and will be updated.