Nearly two dozen commuters were injured following an explosion at Parsons Green underground station in west London that police are treating as terrorism.
Witnesses described seeing people with burns and, separately, wounds caused when passengers rushed to escape the station.
:: Follow updates on our live blog
NHS England said 22 people were taken to hospital, though none were in a serious or life-threatening condition, London Ambulance Service said.
The incident is now being treated as terrorism-related, the Metropolitan Police said. Armed police are at the station and surrounding homes are being evacuated.
Downing Street said Theresa May was “receiving regular updates’’. The PM will chair a meeting of the Government’s emergency Cobra committee this afternoon.
She said: “My thoughts are with those injured at Parsons Green and emergency services who are responding bravely to this terrorist incident.”
The Met’s assistant commissioner, Mark Rowley, said the explosion was caused by an “improvised explosive device”. Most of the 18 casualties suffered “flash burns”, he said.
Police had “many urgent enquiries ongoing” and were working with MI5 intelligence experts, he added.
Reports claimed the explosive device was attached to a timer.
US President Donald Trump tweeted a claim that the “loser terrorist” was among those “in the sights of Scotland Yard”.
He used the attack to call for tougher measures on extremists including “cutting off” the internet and tightening his travel ban.
He said: “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!
“Loser terrorists must be dealt with in a much tougher manner.The internet is their main recruitment tool which we must cut off & use better!
“The travel ban into the United States should be far larger, tougher and more specific-but stupidly, that would not be politically correct!
“We have made more progress in the last nine months against ISIS than the Obama Administration has made in 8 years.Must be proactive & nasty!”
Witnesses told of an “extremely heavy police presence” outside the station. A number of injuries had stemmed from a crush of people trying to leave the station.
Social media reports claimed a bag had exploded, with pictures showing smouldering debris on a District line train. One apparent witness claimed: “Fireball flew down carriage and we just jumped out open door.”
Images showed a white bucket—seemingly with wires trailing from it—inside what appeared to be a Lidl supermarket freezer bag.
Investigators said the device did not fully detonate.
BBC News presenter Sophie Raworth said she saw a woman on a stretcher with burns to her face and legs, the broadcaster reported.
Media technology consultant Richard Aylmer-Hall, 53, was sitting on the District Line train bound for central London when panic unfolded at about 8.20am. Several people were injured after passengers tried to escape, he said.
He added: “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.
“Some people got pushed over and trampled on, I saw two women being treated by ambulance crews.”
Daniel Holden, a Merton borough councillor, told the London Evening Standard he experienced “a loud bang, heatwave and fire burst”.
Aerial images showed passengers being taken off the train.
Ryan Barnett was caught up in the crush that took place in the tube station’s stairwell. He said he heard of victims with burn injuries and reported seeing some commuters taking selfies on the platform.
The 25-year-old, who works in politics and had been travelling to his office, said: “I was lucky, I wasn’t in the carriage, I was in a few carriages down but I was caught up in the stampede down the stairs.
“I was sitting there, headphones in, at Parsons Green, the doors open fine, I’m not really paying attention and all of a sudden hundreds of people run past me screaming a mixture of ‘stampede’, ‘attack’, ‘terrorist’, ‘explosion’, ‘get off the train’, ‘everyone run’.
“Parsons Green station has a staircase at the front of the carriage where the train pulls up – I’m running and keeping my head down because there might be gunfire and on to the staircase.
“But when I was on the staircase, the stewards and other passengers, they are shouting ‘stop, stop, stop’, so I ended up squashed on the staircase, people were falling over, people fainting crying, there were little kids clinging on to the back of me.”
A London Fire Brigade spokeswoman said: “The brigade was called at 8.21am. Fire crews from Fulham, Wandsworth, Chelsea, Hammersmith and other surrounding fire stations are in attendance.”
Six fire engines and about 50 firefighters, plus specialist officers, were sent to the station, she said.
Tube services between Wimbledon and Edgware Road are suspended.
London mayor Sadiq Khan said he was in contact with police over the incident. He said: “Our city utterly condemns the hideous individuals who attempt to use terror to harm us and destroy our way of life.
“As London has proven again and again, we will never be intimidated or defeated by terrorism.”
