Fire crews are battling a large blaze at a warehouse which has sparked explosions and sent huge plumes of smoke billowing into the sky.
Eyewitnesses have reported hearing multiple explosions after the fire broke out at a container storage yard in west London.
Dramatic video and photos posted online show a wall of black smoke drifting across a rail line near West Drayton station.
Other photos show smoke filling the sky just north of Heathrow Airport.
A spokesperson for the airport said flights were operating as normal despite the thick smoke seen across the area.
Trains through the station were reportedly delayed just as the London Marathon came to a close.
Six fire engines and about 40 firefighters have rushed to the blaze in West Drayton, Hillingdon after the alarm was raised just after 2pm.
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One eyewitness told the Mirror: “There were what looked like armed police in the street closing off the roads and getting everybody back - they all had all the proper gear on.
“There's smoke everywhere, it was properly scary.”
One local said on Twitter that her flat shook a number of times following the explosions.
Another said he had counted about nine fire engines at the scene of the blaze and claimed they had all arrived within 15 minutes of the first flames being spotted.
Twitter users posted photos and video of black smoke drifting through West Drayton.
A Twitter user wrote: God hope everyone is ok. This seems like a massive fire. We can here the explosion from a far. West Drayton area."
Another user wrote: "Why have you got trains still running through West Drayton past this trackside fire with the sounds of things clearly exploding?"
A spokeswoman for the London Fire Brigade said: "Six fire engines and around 40 firefighters have been called to a fire at a warehouse in Wimpole Road in West Drayton.
"A container storage yard is alight.
"The fire is very visible and is producing a lot of smoke.
"Residents and businesses in the area should keep their windows and doors shut.
"The Brigade’s 999 control officers have taken 54 calls to the fire.
"Around 15 people left the yard before the arrival of the Brigade.
"There are no reports of any injuries.
"The Brigade was called at 2.16pm.
"Fire crews from Hillingdon, Heathrow, Feltham and other surrounding fire stations are at the scene."
A Met Police spokesman said officers are assisting with road closures.
