Thousands of passengers are facing delays and cancellations after a massive fire ripped through an electricity substation near Heathrow Airport. Up to 300,000 customers were set to fly through Europe’s biggest airport on Friday, with around 1,351 flights affected by the mysterious blaze. After initially saying it would be closed until 11.59pm on, Heathrow gave an update that it will “begin some flights later today”, focusing on repatriation flights for passengers diverted to other airports in Europe. It came after ten fire engines rushed to Nestles Avenue, Hayes, a suburban street around five miles north of the airport, where 70 firefighters tackled the inferno throughout the night from 12am, London Fire Brigade said. An estimated 67,000 households suffered power cuts. About 5,000 were still without power later on Friday. Around 150 residents were evacuated from nearby properties and a 200-metre cordon was put in place around the substation, police said. Here, The Independent takes a look at all we know about the fire about how it has affected flights going in and out of Heathrow Airport. What caused the fire? The Metropolitan Police said its Counter Terrorism Command was leading the investigation into the fire “given the impact this incident has had on critical national infrastructure.” The force said there was “no indication of foul play” but “we retain an open mind at this time”. Footage showed the fire ripping through a Scottish and Southern Electricity Networks-managed substation throughout the night, as dozens of firefighters rushed to extinguish it. One nearby resident described their room shaking and hearing a “loud bang” as the substation caught fire. Energy minister Ed Miliband told BBC: “It's obviously an unprecedented event, but we will want to understand both the causes of this event and what lessons, if any, it can teach us.” What is the economic impact? Air transport consultant John Strickland said Heathrow’s closure will cost the aviation industry millions of pounds. “It will run into millions. You can’t quantify it yet. Heathrow has normally about 200,000 passengers a day, so it’s a massive impact in lost revenues and disruption costs,” he said. British Airways owner International Consolidated Airlines Group (IAG)’s share price had plunged four per cent on Friday morning - equivalent to losing more than half a billion pounds in market capitalisation by 8.30am GMT. How many passengers have been affected? Up to 291,000 passengers were set to fly from Heathrow Airport on Friday, with 1,330 flights scheduled throughout the day, according to aviation analytics firm Cirium. Up to 665 departures were scheduled, equating to over 145,094 seats, and 669 flights were due to arrive, equating to 145,836 seats. British Airways chief executive Sean Doyle said the event would have a huge impact on customers in coming days. “To give you an idea of the scale of disruption we face which we’re working to minimise, today we were due to operate more than 670 flights carrying around 107,000 customers, with similar numbers planned over the weekend,” he said. EasyJet said it was putting larger aircraft on key routes on Friday and over the weekend to provide additional seats to help customers affected by the Heathrow closure. Ryanair has also put on extra flights from Dublin to London Stansted "to rescue passengers affected by today’s Heathrow closure”. When will Heathrow reopen? Heathrow airport said it will “begin some flights later today”, focusing on repatriation flights for passengers diverted to other airports in Europe. The airport originally announced early on Friday that it would be closed until 11.59pm. A Heathrow spokesperson said in an update on Friday afternoon: “We’re pleased to say we’re now safely able to begin some flights later today. “Our first flights will be repatriation flights and relocating aircraft. “Please do not travel to the airport unless your airline has advised you to do so. “We will now work with the airlines on repatriating the passengers who were diverted to other airports in Europe. “We hope to run a full operation tomorrow and will provide further information shortly.”