A rush hour blast caused by an improvised explosive device on a London Underground train which injured 22 people is being treated as terrorism by London's Metropolitan Police.
None of the injured are thought to be in a serious or life-threatening condition, according to the London Ambulance Service.
"We now assess that this was a detonation of an improvised explosive device," Metropolitan Police Assistant Commissioner Mark Rowley said at a press conference. Most of the injuries appear to be the result of flash burns, he said.
Asked by a reporter if police had any information on the perpetrator, Rowley said: "It's a live investigation." Hundreds of detectives are working on the inquiry with the support of Britain's domestic intelligence service, MI5.
A police officer escorts an injured woman from the scene at Parsons Green Underground Station. Several people have been injured after an explosion on a tube train in south-west London. The Police are treating the incident as terrorism.
Downing Street tweeted a message from Prime Minister Theresa May, saying: "My thoughts are with those injured at Parsons Green and emergency services who are responding bravely to this terrorist incident."
"Suddenly, there was this boom," eyewitness Gustavo Vieira told CNN. "Everyone shouting and screaming... We were just leaving the carriage [when the explosion happened]... Just heard and everyone starting running... And I didn't look back."
Police arrested an 18-year-old man Saturday morning in the port area of Dover. On Saturday afternoon, police evacuated a residential address and surrounding buildings in Sunbury-on-Thames, Surrey, to the west of London, as they carried out a search in connection with the attack (pictured).