A fire broke out on a London subway train Friday, leaving passengers choking on smoke and sparking the rush-hour evacuation of one of the busiest stations on the transit network.

Firefighters dealt with a small blaze aboard a Bakerloo Line train at Oxford Circus station, and paramedics treated four people for smoke inhalation, taking two of them to a hospital as a precaution, authorities said.

Passengers said staff ordered everyone to leave the station just before 9 a.m. (0800 GMT) as smoke billowed from a train.

Passenger Tom Singer tweeted a photograph of smoke filling a carriage and spilling onto a platform. Another photo posted by Joe Bunting showed passengers in a smoky subway car covering their mouths and noses.

Police said the cause "is not currently being treated as suspicious."