An explosion was recorded in one of the subway cars which injured several people as it toured the Green District at the Parsons Green stop in London.
Originally the British authorities handled the case as "an incident", but hours later it was confirmed as a terrorist act.
— Sylvain Pennec (@sylvainpennec) September 15, 2017
Several witnesses told El País portal that there were several burn injuries and that there was a stampede at the station at 8:30 am (local time) at the time of greatest influx.
It was also reported that the London ambulance service moved 18 injured people to different hospitals, although none in serious condition.
The injured had burns, cuts and blows when trying to flee the station.
— London Ambulance (@Ldn_Ambulance) September 15, 2017
Some of the passengers reported that the explosion had its origin in a white cube that contained a plastic bag.
The Metropolitan Police published in its official account of Twitter that the incident was declared "terrorist".
"We received reports at 8:20 am of a fire on the train at Parsons Green station."
The blast comes as Britain is on high alert after four terrorist attacks so far this year.
The incident recalls that on July 7, 2005, a series of jihadist suicide bombings took place on the London network that left 52 dead and more than 700 wounded.