An “improvised explosive device” was detonated on a Tube train in south-west London during Friday’s rush hour, has reported by the BBC.
The blast, at Parsons Green station on an eastbound District Line train from Wimbledon, is being treated as terrorism.
Twenty-two people are being treated in hospital, mostly for burn injuries.
A hunt for the person who placed the device is under way, with hundreds of detectives and MI5 investigating.
Assistant Commissioner Mark Rowley earlier refused to reveal whether anyone had yet been arrested.
Pictures taken of the train show a white bucket on fire inside a supermarket bag, with wires trailing on to the carriage floor.
The BBC understands the device had a timer.
BBC security correspondent Frank Gardner said the incident could have been “far worse” as indications were that the bomb “may have partially failed”.
He said intelligence services would be reviewing whether to raise the national terrorism level from severe – the second highest – to critical, the highest threat, which means an attack is expected imminently.
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.”
A meeting of the government’s emergency committee, Cobra, has recently finished.
Mayor of London Sadiq Khan has appealed for calm, saying the city “will never be intimidated or defeated by terrorism”.
US President Donald Trump tweeted: “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!”
Culled from bbcnews.com