Twenty-seven people - mostly teenagers and young people - have been killed after fire broke out at a nightclub in Bucharest, officials say, according to BBC News.

The blaze took hold at the Colectiv club on Friday, October 30 night, causing a stampede for the exit.

Emergency response chief Raed Arafat said 155 people were being treated in hospitals in the Romanian capital.

The fire is believed to have been caused by fireworks that were let off inside the club. The pyrotechnics were reportedly part of a show by a heavy metal band.

Witnesses said a spark on the stage ignited some of the polystyrene decor. A pillar and the club's ceiling caught fire and there was an explosion and heavy smoke, they added.

Up to 400 people may have been inside the club, which was hosting a free rock concert.

Local journalist Sorin Bogdan told the BBC the club was in a converted former factory with two small exit doors, only one of which was possible to open initially.

A witness quoted by Romania's state news agency said terrified concert-goers had to break the second door down to escape.

Prime Minister Victor Ponta said he was cutting short a visit to Mexico to return to Bucharest.

Romania's President Klaus Iohannis wrote on his Facebook page that he was "deeply grieved by the tragic events that happened this evening in downtown."