Dozens of Tube commuters have been evacuated through a tunnel amid reports of smoke on a train.
Fifty-nine passengers were escorted off the Jubilee Line service after it stopped between Bond Street and Baker Street stations.
Four people were treated at the scene for smoke inhalation, but were not taken to hospital.
Firefighters said a mechanical failure may have caused the smoke, while police said there was no fire onboard.
The line was shut between Finchley Road and Waterloo throughout the rush hour.
Transport for London said an investigation had been launched into the cause of a “track fault” at Bond Street.
A spokeswoman apologised for “any distress and disruption” caused by the evacuation.
Four crews of firefighters – from Soho, Paddington and North Kensington fire stations – were called at 05:54 BST and left at 07:18.
A spokesman for London Ambulance Service said “a number of resources” were sent to Bond Street station including a specialist hazardous area response team.
He added: “no patients were taken to hospital”.