Thousands of travelers have been impacted by a power outage at London's Heathrow airport Friday, due to the result of a massive fire the day prior.

The fire started in a transformer in an electrical substation in the town of Hayes, in west London. At least 10 fire engines and about 70 firefighters have responded to the blaze, the London Fire Brigade said.

The cause of the fire has yet to be identified.

Hundreds of flights have been canceled or rerouted due to the incident and multiple people had to be evacuated from the airport.

The Metropolitan Police in London said it had counterterrorism specialists leading the investigation, according to The New York Times.

While the fire is reportedly under control, the airport is completely shut down due to the power outage.