Heathrow Airport has reopened for a limited number of flights after a large fire at a nearby electrical substation disrupted travel for around 200,000 passengers.

Counter-terror police were among the agencies that have been investigating the cause of the blaze, which triggered a “significant power outage” that led to more than 1,000 flights to and from the airport being cancelled.

The Metropolitan Police said on Friday evening that the cause of fire is believed to be non-suspicious, while the London Fire Brigade announced its investigation will now focus on the electrical distribution equipment.

National Grid said an “interim solution” had been found to restore supplies to customers including Heathrow Airport.

Follow live updates on Heathrow closure

Just after 4pm, a Heathrow spokesperson said the airport was “safely able to begin some flights later today”.

The first flights will be repatriation flights and relocating aircraft, with Heathrow working with airlines to bring back the passengers diverted to other airports across Europe.

“We hope to run a full operation tomorrow and will provide further information shortly,” the spokesperson added.

“Our priority remains the safety of our passengers and those working at the airport. As the busiest airport in Europe, Heathrow uses as much energy as a small city, therefore getting back to a full and safe operation takes time. We apologise for the inconvenience caused by this incident.”

The first flight to land at Heathrow since the closure touched down just after 6pm.

The British Airways BAW35JG flight arrived from Gatwick Airport.

Meanwhile, British Airways said eight long-haul flights will depart from Heathrow from 7pm, with the airline “urgently contacting customers” to tell them to come to the airport.

The only customers who should make their way to Heathrow Airport are those booked onto the following flights: BA055 to Johannesburg, BA057 to Johannesburg, BA011 to Singapore, BA259 to Riyadh, BA045 to Cape Town, BA059 to Cape Town, BA015 to Sydney via Singapore, and BA249 to Buenos Aires via Rio de Janeiro.

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Airport disruption nearly ‘as big as it gets’

Heathrow Airport’s chief executive Thomas Woldbye has told reporters the flights taking off this evening will help make sure the airport has “operations in place for tomorrow morning”.

He continued: “Tomorrow morning we expect to be back in full operation, so 100% operation as a normal day.”

Mr Woldbye added that passengers who were planning to fly from Heathrow tomorrow should come to the airport in time for their flight as normal.

The chief executive also apologised to the passengers whose journeys had been disrupted but said he would not have closed down the airport unless there were “severe safety concerns”.

Asked whether the disruption caused by the fire suggested there was a “weak point” in Heathrow’s operations, Mr Woldbye replied: “We can’t guard ourselves 100%. This has been a major incident.

“Short of anybody getting hurt, this is as big as it gets for our airport and we are actually coming back quite fast.”

He added: “This is unprecedented, it’s never happened before.”

It comes after Number 10 said earlier that there are questions to be answered about how the fire has caused so much chaos.

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Mr Woldbye said: “Our procedures have worked the way they should… Of course the prime minister should ask questions and we’ll be happy to answer them.”

Earlier, the airport said it expected “significant disruption over the coming days” and warned passengers “not travel to the airport under any circumstances until the airport reopens”. All trains to Heathrow were suspended.

Some power has returned to Terminal 4, with lights in the main building and lifts in the multi-storey car park operational again.

The disruption began late on Thursday night when fire crews were called to a blaze in west London at an electricity substation serving Heathrow and local properties.

Thousands of passengers stranded

Heathrow is one of the world’s busiest airports and had a record 83.9 million passengers last year, with a plane landing or taking off around every 45 seconds.

The figure, from the Civil Aviation Authority, is equivalent to about 229,000 passengers using the hub every day.

Meanwhile, Aviation analytics firm Cirium told the New York Times that it believes as many as 290,000 passengers could be affected today – enough to fill Wembley Stadium three times.

Oil fire still alight at substation

The fire that caused the power outage is at the North Hyde substation in Hayes, about 1.5 miles to the north of the airport.

London Fire Brigade’s (LFB) deputy commissioner Jonathan Smith told reporters at a news conference the fire involved a transformer – a key part of the substation – with 25,000 litres of cooling oil “fully alight”.

Crews evacuated 29 people from neighbouring properties but there were no casualties.

In all, 67,000 households were left without power after the fire at the substation, but all supplies have been restored.

Earlier LFB said 10 engines and around 70 firefighters had been working to extinguish the blaze – with the first 999 call received at 11.23pm on Thursday.

Pictures from the scene showed large flames and plumes of thick black smoke.

The LFB said in a statement that 5% of the fire was still alight as of 7pm this evening.