London attack – as it happened: Theresa May raises threat level to critical as Isis claims responsibility

Aimee Caulfield, who works here at The Independent, was on the train behind the one that was rocked by the explosion. She said that was only told that there had been an incident, and after a long wait to get into the station they were taken to Parsons Green, where everyone panicked.

"It was chaotic," she said. Everyone was running out. Trying to get out of the stairs as quickly as possible. No-one knew what was going on. Some people wanted to wait – they thought it was just a signal failure."

Theresa May says her "thoughts are with those injured at Parsons Green and the emergency services who, once again, are responding swiftly and bravely to a suspected terrorist incident".

London mayor Sadiq Khan has released a statement on his Facebook page:

The Metropolitan Police have confirmed that the explosion on a train at Parsons Green Station this morning is being treated as terrorism.

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.

I am in close contact with the Metropolitan Police, Transport for London, Government and other emergency services who are responding at the scene and leading the investigation. I will be attending the emergency COBRA meeting in Whitehall this afternoon with the Prime Minister.

My sincere gratitude goes to all our courageous emergency responders and the TfL staff who were first on the scene.

I urge all Londoners to remain calm and vigilant, and to check TfL’s website for travel advice.

A major incident has been declared at St Mary's Hospital in Paddington in response to the Parsons Green explosion.

The wires that look to be trailing from the flaming bucket seen in pictures appear to be fairy lights. That might be significant, since another man was convicted of plotting to use fairy lights and a pressure cooker as part of a bomb plot earlier this year.

Here's some information from Lizzie Dearden on the – apparently untrue – reports that a man is on the run with a knife.

People being evacuated from an exercise class near the Tube station said a police officer told them a man was on the loose with a knife. But the report was not repeated by other officers and witnesses said they thought the officer may have been misinformed or trying to get them to evacuate more quickly.

Chris Wildish, who was on London subway train where a fire occurred that is being treated as terrorism, said he saw "a massive flash of flames" that reached up to the ceiling of the train and then the air was filled with the smell of chemicals. Wildish told Sky News that many of the passengers were schoolchildren, who were knocked around by people trying to get away from the fire. 

Wildish said he saw several burned passengers and later, during evacuation of the station, caught sight of a bucket still in flames. 

Footage filmed from the platform through the train door as people were evacuated shows flames licking from the bucket, which is inside a plastic shopping bag. "That bag's on fire," a woman exclaims, before a London Underground staff member orders commuters to get away from the carriage to the end of the platform.

From the Press Association:

Ryan Barnett was caught up in the crush that took place in the stairwell of the Tube station.

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, told the Press Association: "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.

"It is absolute chaos, it was quite scary because at one stage we thought we might be trapped there - I heard a pregnant woman lost her shoes and had fallen over."

Ferried back on to the station platform, Mr Barnett began hearing from others around him about the state of those injured.

He said: "Someone said there had been an explosion, there was white stuff, someone said there was a lot of wires, one girl outside the station had her leg pretty badly cut up.

"People were saying there was one man who was singed down the side of his body, including his hair.

"It felt like an eternity, but it was only a couple of minutes, probably.

"There were a lot of people taking photos, there was a couple of people taking selfies and I thought: 'What is the world coming to?"'

Olaniyi Shokunbi, 24, boarded the train the bomb had been planted on at Putney Bridge and had been listening to music when he saw people scrambling off the train.

He said: "I thought the train was leaving Parsons Green but then I saw lots of people running up.

"My first instinct was to get out of the train myself.

"It's a small station. There's only two exits and a lot of people were struggling over each other. Some people just jumped over.

"I thought it was an acid attack. It was early morning and people were drinking coffee and I felt some [liquid] on me and I thought 'that better not go on my face'."

Mr Shokunbi, a fitness instructor, said he had seen people lying on the floor covered in blood.

He said: "There were people on the floor, there was a little boy, I really felt sorry for him, he couldn't have been more than 11.

"He had scratches on his head, he was looking for his little brother.

"I was going to go back into the train station but a woman said 'don't go back in there, there's people on the floor'."

He added: "There was a woman on the floor. She couldn't breathe. People were screaming and crying."

This is from Lizzie Dearden:

Mark Arnell, the director of Ride Republic, was leading a spinning class near the station when the explosion struck.

"A man came running in and said there had been a terror attack and everyone needs to get out," he said.

"Then the police came - the first one said we needed to leave or to get downstairs and hide, then the second one told us to evacuate.

"We got outside and police were banked all down the road and outside the school (Kensington Prep).

"People were running down the road and people were crying, there were loads of children."