Three people have been treated for breathing difficulties after a Tube train became stranded in a tunnel and its carriages filled with smoke.
The Northern Line train drew to a halt outside Bank station where it remained for 10 minutes on Thursday.
Fire crews treated one man and two members of staff for smoke inhalation.
A Transport for London spokesman said Bank station was evacuated, adding the smoke might have been caused by sparks from track insulation.
He said Northern Line services were suspended and, as is routine, London Bridge station was also evacuated.
London fire crews were called at 1340 GMT on Thursday to reports of smoke on the platform.