Explosion rocked a District Line Underground train in south- west London on Friday morning.
Emergency services are at the scene of the incident, the BBC reports.
Accrding to report, at least 22 people were injured after a bomb detonated and the police are treating as a “terrorist incident”.
Witnesses reported seeing passengers covered in blood and with facial burns and hair coming off at Parsons Green station in west London after the explosion on the train.
“At 8:20 this morning at Parsons Green station there was an explosion on a Tube train. We now assess that this was a detonation of an improvised explosive device,” police counter-terror chief Mark Rowley said.
The incident is the fifth terror attack in six months in Britain since March, when a lone attacker mowed down pedestrians and stabbed a police officer outside the British parliament.
London Mayor Sadiq Khan urged Londoners to remain “calm and vigilant”.
“As London has proven again and again, we will never be intimidated or defeated by terrorism,” he said in a statement.
US President Donald Trump said the attack was carried out by a “loser terrorist”.
“These are sick and demented people who were in the sights of Scotland Yard. Must be proactive!” he said on Twitter, without explaining further.