An explosion on a London Underground train has left commuters with "facial burns" after a "fireball flew down a carriage", reported the British newspaper The Sun.

Emergency services are at the scene in South London with early reports suggesting several are injured amid widespread panic.

There are reports of people fleeing the scene screaming with a Metro reporter saying people are "really badly burned" adding that "their hair was coming off".

According to the newspaper, an onlooker said, “a fireball flew down a carriage” with panicked commuters diving out an open door at the South West London station.

Train services through the area have been halted with commuters reporting they were informed of a "security incident".