Several people were injured when a bomb exploded on a packed rush-hour commuter train at a London underground station on Friday, according Reuters.

Emergency services said they had been called to reports of a fire on a train at Parsons Green station in West London at 8.20 a.m. (0720 GMT)

“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,” London police said in a statement.

Commissioner Neil Basu, the senior national coordinator for counter-terrorism policing, had declared it a terrorist incident, the statement said.

An unverified picture circulating on social media showed a white bucket with a supermarket freezer bag on the floor of one train carriage. The bucket was in flames and there appeared to be wires coming out of the top.

“I was on second carriage from the back. I just heard a kind of whoosh. I looked up and saw the whole carriage engulfed in flames making its way towards me,” Ola Fayankinnu, who was on the train said.

“A lot of people were trampled on. There were phones, hats, bags all over the place and when I looked back I saw a bag with flames. People were crying, shocked, a few people had been injured, some people had been trampled.”