Reports of passenger on the track causes Jubilee line problems on Underground
The Jubilee line was suspended on Wednesday morning after passengers and a train driver heard cries for help.
Services were stopped between Waterloo and Finchley Road as the power was turned off and emergency services investigated the scene.
Severe delays are currently on all other parts of the line.
The incident happened at Bond Street.
A Transport for London spokeswoman said: "People on the train and the driver heard calls for help while the train was in the station."
Emergency services will first check under the train and then inside the tunnel.
10AM UPDATE: The line was reopened and running with minor delays.