Thousands of travellers on Friday saw their travelling plans disrupted and unable to make their trips into and out of the United Kingdom after a fire caused by a power outage at Heathrow Airport forced the closure of the usually busy airport.

According to the New York Times, Heathrow officials said the airport was expected to remain closed for more than 22 hours, running to midnight, but travel disruptions were expected to last into the weekend after dozens of flights into the airport were cancelled or turned around.

The cause of the fire that broke out in the airport’s electricity substation overnight remains unclear, but London’s Metropolitan Police Service said its counterterrorism unit had swooped in to lead investigations into the blaze.

Meanwhile, Sadiq Khan, the Mayor of London, downplayed the involvement of counterterrorism officials, saying it is not “unusual” for them to be present where there are major fire incident events, adding that “there is no reason at all for anyone to be concerned or alarmed in relation to the fire at the substation.”

Ed Miliband, Britain’s energy secretary, also shared a similar view while speaking on the incident, stating “no suggestion there is any foul play,” but added, “We don’t yet have a real understanding of what caused the fire.”

Mr Miliband added that the outage had also knocked at least one backup generator, leaving the majority of the airport without power.

Heathrow Airport is one of the busiest in the world, with more than 230 destinations in over 90 countries. It hosted about 83.9 million passengers last year, with an average of 229,000 passengers daily, higher than pre-pandemic levels.