Whatever caused the fire near Heathrow Airport, the scale of the chaos raised uncomfortable questions for Britain’s government about issues such as the security measures protecting key transport hubs and the resilience of the country’s often aging infrastructure.

With counterterrorism police leading the investigation, the possibility of sabotage was being taken seriously, at least as a precaution, though officials say there is currently no evidence that foul play was behind the blaze at the electricity substation.

The Metropolitan Police in London said that counterterrorism specialists had taken charge “given the location of the substation and the impact this incident has had on critical national infrastructure.”

Sadiq Khan, the mayor of London, said that it was “not unusual” for the specialized officers to be involved in an investigation of such a major incident, and he told Sky News that there was “no reason at all for anyone to be concerned or alarmed.”

Nonetheless, with the fire still burning and threatening to extend the disruption into Saturday, nothing has been ruled out.

In a statement, Prime Minister Keir Starmer of Britain said that he was “receiving regular updates” about the situation at Heathrow and was “in close contact with partners on the ground.” He added that he knew the outage was “causing distress and disruption, especially for those traveling or without power in their homes.”

Heidi Alexander, the British transport secretary, said that she had spoken to managers at Heathrow and had been “reassured they are working tirelessly to reopen the airport as soon as possible.”

But there seemed to be no certainty that the inconvenience for travelers would end quickly. Asked at a news briefing whether there was confidence that the airport would reopen at midnight, a Downing Street spokesman said that it would be up to the emergency services and Heathrow to decide, but he acknowledged that there would be significant disruption in the hours and days ahead.

Another question was whether a meeting would be convened on Friday afternoon of a government emergency response committee, known as COBRA (an acronym for Cabinet Office Briefing Room A). If it is, that could be a signal that the closure of the airport was expected to last into Saturday.

John McDonnell, a lawmaker who represents Hayes, the area where the fire broke out, said that any investigation would need to look at “why backup arrangements have not worked” and how the infrastructure could be so vulnerable.

“There are lessons that have got to be learned here,” he told reporters on Friday afternoon.