London's Heathrow Airport has announced that it will be closed all day on Friday due to a major power outage caused by a fire at an electrical substation.

Britain's key airport said on social media early on Friday, local time, that it would be closed until 11:59 pm.

The flight-tracking website FlightRadar24 shows many inbound flights diverting to other airports. It says the closure will affect more than 1,300 flights to and from the airport.

Reuters news agency cited a Heathrow spokesperson as saying it is not clear when power will be restored, and that significant disruptions are expected over the coming days.

The airport has advised passengers to avoid it in their travel plans and urged them to contact their airlines for further information.

Heathrow Airport's website says it is the second busiest airport in the world, and the busiest in Europe. The incident has raised concerns about its possible effects on passenger traffic and international air cargo.

 nhk