London: Heathrow Airport will resume some flights on Friday evening (UK time) after being closed for much of the day following a power outage which upended journeys for hundreds of thousands of passengers.

The airport, one of the busiest in the world for international traffic, said it expected significant disruption for days. As of late afternoon local time, it said it was gearing up to restart flights.

The power outage was caused by a fire at an electrical substation supplying the airport. Police said while there was no evidence at this stage of foul play, counter-terrorism officers would lead the probe because of the incident’s impact on critical infrastructure.

“We’re pleased to say we’re now safely able to begin some flights later today. Our first flights will be repatriation flights and relocating aircraft,” a Heathrow spokesperson said. The first flights would be to relocate aircraft and to bring passengers who had been stranded at other airports to London, they said.

London’s Metropolitan Police said all possible lines of inquiry were being pursued, while Downing Street has said there were “questions to answer” over how a single fire had been able to shut down Heathrow.

About 120 aircraft were en route to Heathrow when the fire broke out, according to aircraft tracking specialist Flightradar24. Those flights have been diverted. At least 1350 flights to and from the airport were affected.

Passengers on board Qantas flights to Heathrow Airport from Singapore and Perth on Friday were diverted to Paris before taking buses to London, the airline said.

Mag Leahy told The Telegraph she and other passengers were forced to take a coach through the Channel Tunnel and finally arrived at Heathrow on Friday evening.