A total of 22 people - including children - were injured in the explosion, with a lot of them suffering from "flash burns and are being treated in hospital, mostly for burn injuries".
- Passengers on board the train fled as fire engulfed a carriage at Parsons Green underground station in West London at 8.20 am (0720 GMT). "It happened just as we were pulling up to the Tube station so everyone just sort of piled out of the Tube, and there was a distinct smell of burning", one witness, identified only as Luke, told the BBC. As a manhunt takes place across the capital, authorities have tightened security on all transport hubs, The New York Times reports.
"People started to run but we were lucky to be stopping at Parsons Green as the door started to open".
Police say they are aware of several people injured.
Pictures on social media showed a white bucket on fire inside a supermarket bag but did not appear to show extensive damage to the inside of the train carriage, the BBC reported.More news: US Congress sends anti-white supremacist resolution to Trump
The underground operator said services have been cut along the line.
Britain's official threat level stands at "severe", the second-highest rung on a five-point scale, meaning an attack is highly likely.
According to the health service, 22 people are injured in the terror attack.
The attack drew swift condemnation from U.S. President Donald Trump.
The police bomb squads and fire crews remained at the scene including London Ambulance's Hazardous Response Units.
Islamic State claimed responsibility as well as for a June attack near London Bridge which left eight dead.