A witness has told how “panic” unfolded on a London Underground train after a makeshift bomb was detonated, with passengers screaming and desperately trying to escape.

The attack on a packed out District line service at Parsons Green in west London around 8.20am today is being treated as an act of terrorism.

Britain’s top counter-terror officer Mark Rowley said: “We now assess this was a detonation of an improvised explosive device.”

Eighteen people were injured in the explosion, with most of them suffering flash burns.

East Anglian Daily Times: Handout photo issued by Sylvain Pennec of a bucket on fire on a tube train at Parsons Green station. Picture: Sylvain Pennec/PA WireHandout photo issued by Sylvain Pennec of a bucket on fire on a tube train at Parsons Green station. Picture: Sylvain Pennec/PA Wire

Prime Minister Theresa May is to chair a meeting of the Government’s Cobra emergencies committee this afternoon to discuss the incident.

Pictures appear to show flames and wires in a bucket which had been carried in a supermarket freezer bag.

Media technology consultant Richard Aylmer-Hall, 53, was sitting on the train, which was bound for central London, when the incident happened.

He told the Press Association: “I was blissfully reading my paper and listening to a podcast and suddenly the whole world charged past me down the platform, down the Tube.

“I was on the Tube, we had just stopped at Parsons Green, I was on my way up from Wimbledon towards Paddington and suddenly there was panic, lots of people shouting, screaming, lots of screaming.

“There was a woman on the platform who said she had seen a bag, a flash and a bang, so obviously something had gone off.

“It was an absolutely packed, rush-hour District Line train from Wimbledon to Edgware Road.

“I saw crying women, there was lots of shouting and screaming, there was a bit of a crush on the stairs going down to the streets.

“Some people got pushed over and trampled on, I saw two women being treated by ambulance crews.”

US President Donald Trump denounced the attack on Twitter saying: “Another attack in London by a loser terrorist. These are sick and demented people who were in the sights of Scotland Yard. Must be proactive!”