The UK's largest airport is closed for the day after a fire at an electrical substation left thousands of homes without power and disrupted Heathrow itself.
"Heathrow is experiencing a significant power outage across the airport due to a large fire at a nearby electrical substation," a spokesperson said.
"Whilst fire crews are responding to the incident, we do not have clarity on when power may be reliably restored. To maintain the safety of our passengers and colleagues, we have no choice but to close Heathrow until 23h59 on 21 March 2025.
"We expect significant disruption over the coming days and passengers should not travel to the airport under any circumstances until the airport reopens.
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“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.”
Over 1,300 flights and 200,000 passengers are expected to have their journeys disrupted by this as Heathrow is the UK's biggest airport and one of the world's busiest.
The extent of the disruption is laid bare when looking at sites such as Flightradar24, which show that in the skies above London the only things going around Heathrow are a couple of news helicopters buzzing over the closed airport.
Instead, Gatwick is a veritable hive of activity as flights that would have been bound for Heathrow are rerouted there.
Along with Gatwick, radar sites showed flights being redirected to Charles de Gaulle Airport in Paris and Shannon Airport in the Republic of Ireland.
Scottish and Southern Electricity Networks have said they want to get power back on by 3pm today (21 March), but the prior announcement from Heathrow indicates they're not expecting to reopen until midnight at the earliest.
The chaos isn't expected to stop immediately when Heathrow is back up and running, either.
With so many flights and passengers affected other airports will have to take the strain and those journeys will need to be squeezed in among the usual influx of air travellers.
If passengers don't want to get a refund and call their journey quits, then airlines need to sort alternative travel for them which will disrupt lots of other journeys as well.
For those of you fretting over whether you'll be able to claim anything with your travel plans thrown into disaster, we have some good news and bad news.
The good news is you're likely to be able to demand a refund from your airline or have them sort another way of getting you where you need to be.
The bad news is that these are likely to be 'extraordinary circumstances' so compensation is unlikely to be on the cards.
Joe Harker