Emergency services are at the scene of a reported explosion on a District Line Underground train in south-west London.
A picture on social media showed a white bucket inside a supermarket bag, but does not appear to show extensive damage in the carriage.
Witnesses described seeing at least one passenger with facial injuries.
Others have spoken of “panic” as alarmed passengers left the train at Parsons Green station at around 08:20 BST (07:20 GMT) on Friday morning.
London Ambulance Service says it has sent a hazardous area response team to the scene.
BBC London presenter Riz Lateef, who was at Parsons Green on her way in to work, said: “There was panic as people rushed from the train, hearing what appeared to be an explosion”
“People were left with cuts and grazes from trying to flee the scene. There was lots of panic”
BBC News presenter Sophie Raworth says she saw a woman on a stretcher with burns to her face and legs.
Alex Littlefield, 24, a City worker, said: “I was walking around the corner to the Parsons Green Tube station and I saw the raised platform with everyone running and looking upset.
“I saw police officers, fire brigade… masses of people and armed police. There were lots of very, very distressed people. We’ve been pushed right back now.”
Media technology consultant Richard Aylmer-Hall who was sitting on the “packed” District Line train said he saw several people injured, having apparently been trampled as they tried to escape.
The 53-year-old said “suddenly there was panic, lots of people shouting, screaming, lots of screaming.
“There was a woman on the platform who said she had seen a bag, a flash and a bang, so obviously something had gone off.
“I saw crying women, there was lots of shouting and screaming, there was a bit of a crush on the stairs going down to the streets,” he said.
Natasha Wills, assistant director of operations at London Ambulance Service, said: “We were called at 8:20 to reports of an incident at Parsons Green underground station.
“We have sent multiple resources to the scene including single responders in cars, ambulance crews, incident response officers and our hazardous area response team, with the first of our medics arriving in under five minutes.
“Our initial priority is to assess the level and nature of injuries. More information will follow when we have it.”
