Emergency Fire crews, paramedics, a bomb squad and counter terror police evacuated train and checked the line for suspect.
Area around Parsons Green tube station have been evacuated. Police have now identified a man via CCTV.. details to be released at a later stage of this LIVE investigation..
1pm UPDATE : Met Police Deputy Assistant Commissioner Neil Basu, the senior national coordinator for CT policing, has declared it a terrorist incident at Parsons Green Underground Station.
It is too early to confirm the cause of the fire, which will be subject to the investigation that is now underway by the Met's Counter Terrorism Command.
The station remains cordoned off and we are advising people to avoid the area.
One witness said: "it was terrifying. A massive flash of flames went up the side of the train with an acrid, chemical smell"
Emma, who was at Parsons Green station, said: "We were running down the stairs like... it felt like for our lives.
"I went down the stairs and after a while people were just piling on top of each other, because people were falling over trying to run so quickly.
"There were two ladies underneath me and a little boy to my right, his head had been smacked into the concrete."
Peter Crowley revealed he recieved minor burns and much of his hair had been singed off.
The device looks deliberate but some media are actually playing it down as an accident!!
Police said they were looking for an armed man said to be on the run with a knife.
A BBC News presenter Sophie Raworth, who was at the scene, said she saw a woman on a stretcher with burns to her face and legs.
'The primary concern is that a man is still at large but there will be good CCTV images of that person' says terror expert.
Transport for London said it is ‘investigating an incident at Parsons Green’ and urged customers travelling between Wimbledon and Earls Court to use alternative routes.
A London Ambulance Service spokesman said: ‘We are on scene alongside the Metropolitan Police at Parsons Green.’
London Fire Brigade said they were called to the incident at 8.21am on Friday.
Anyone who has information that would assist detectives is urged to contact the hotline 0800 789 321; if it's an emergency always call 999.