An explosion on a Tube train in south-west London is being treated as terrorism, Scotland Yard has said.
Passengers were injured in the blast at 08:20 BST at Parsons Green station on the District Line.
Pictures show a white bucket on fire inside a supermarket bag, but do not appear to show extensive damage to the inside of the carriage.
Eighteen people had been taken hospital, the London Ambulance Service said in a statement.
The Metropolitan Police said it was too early to confirm the cause of the fire and the station, which is above ground, has been cordoned off.
Prime Minister Theresa May tweeted: “My thoughts are with those injured at Parsons Green and emergency services who are responding bravely to this terrorist incident.”
The government’s emergency committee, Cobra, is meeting at 13:00 BST.
Mayor of London Sadiq Khan has appealed for calm, saying the city “will never be intimidated or defeated by terrorism”.
Witnesses have described seeing at least one passenger with facial injuries.
Others have spoken of “panic” as alarmed passengers left the train at Parsons Green station.
Passenger Peter Crowley said he was sat in the carriage, traveling eastbound from Wimbledon, when the explosion happened.
He said his head was burned by a “really hot intense fireball above my head” and added: “There were people a lot worse than me.”
Passenger Chris Wildish told BBC Radio 5 live he saw a bucket in a supermarket bag with “low-level flames coming out of it” by the door of the rear carriage.
