London’s Heathrow airport will be closed all day on Friday, sparking global travel chaos, after a fire at an electrical substation caused a “significant power outage” there, and left thousands of homes without power.

The shutdown occurred just hours before the travel hub – one of the busiest two-runway airports in the world – was due to open, forcing at least 120 flights that were already in the air to divert, according to Flightradar24, with more than 1,300 arrivals and departures expected to be affected through the day.

British Airways and Virgin Atlantic diverted flights to nearby Gatwick, which said its flights were operating as normal. On Friday morning, Qantas diverted its Perth-London flight to Paris and a United Airlines New York flight was sent to Shannon, Ireland. Some flights from the US were turning around mid-air and returning to their point of departure.

Neil Hansford, head of the Sydney-based Strategic Aviation Solutions consultancy, said the closure of Heathrow for a day was “unheard of” for the industry, in terms of ramifications for global aviation, since the September 11 terrorist attacks which closed US airspace.

Airlines around the world will be grappling with a “logistical nightmare” to transport customers to diversion airports and manage jet fuel sources and staff displaced by the closure, said Hansford.

While London’s other airports, such as Gatwick and Stansted, would take diverted flights, Heathrow’s scale meant other airports did not have the capacity to absorb all of its operations. “These airports can’t take anything close to the volume of Heathrow’s five terminals, where there’s an arrival every minute,” he said.

“Heathrow is one of the major hubs of the world,” said Ian Petchenik, spokesperson for FlightRadar24. “This is going to disrupt airlines’ operations around the world.”

In a statement on its website and shared on social media, Heathrow airport said all passengers were advised not to travel to the airport. “To maintain the safety of our passengers and colleagues, Heathrow will be closed until 23h59 on 21 March,” the statement said.

An airport spokesperson said: “We will provide an update when more information on the resumption of operations is available. We know this will be disappointing for passengers and we want to reassure that we are working as hard as possible to resolve the situation.”

The fire late on Thursday at an electrical substation in west London left more than 16,000 homes without power, and forced more than 100 people to evacuate. Firefighters led 29 people from surrounding properties to safety.

The London fire brigade said a transformer within the substation was alight, with 10 fire engines and about 70 firefighters on the scene at Nestles Avenue in Hayes.

About 150 people were evacuated from surrounding properties and a 200-metre cordon put in place as a precaution.

Assistant commissioner Pat Goulbourne said: “This is a highly visible and significant incident, and our firefighters are working tirelessly in challenging conditions to bring the fire under control as swiftly as possible.

“The fire has caused a power outage affecting a large number of homes and local businesses, and we are working closely with our partners to minimise disruption.”

The brigade said nearly 200 calls had been received in relation to the incident with crews from Hayes, Heathrow, Hillingdon, Southall and surrounding areas on the scene.

Scottish and Southern Electricity Networks said in a post on X there was a large-scale power outage in the area impacting more than 16,300 homes.

“We’re aware of a widespread power cut affecting many of our customers around the Hayes, Hounslow and surrounding areas,” it said.

Emergency services were called to the scene at 11.23pm on Thursday. The cause of the fire was yet to be determined.

Goulbourne said firefighters urged people to take safety precautions as crews worked to extinguish the blaze. “This will be a prolonged incident, with crews remaining on scene throughout the night,” he said.

“As we head into the morning, disruption is expected to increase, and we urge people to avoid the area wherever possible.”