Urgent safety checks are being carried out on trains running on the Metropolitan line section of the Tube, Transport for London (TfL) has said.
TfL is warning of severe disruption as engineers check over the entire fleet of trains which also run on the Circle and Hammersmith & City lines.
The trains were only introduced in 2010, but TfL said a fault had been identified on some of their wheels.
As a result engineers are increasing the frequency of inspections.
“Safety is our top priority, and as a precautionary measure we have increased the rate of inspection of these trains to make detailed checks of the entire fleet,” a TfL statement said.
Passengers are being advised to check before they travel.
Trains are operating between Baker Street and Amersham or Chesham every 30 minutes, between Watford and Baker Street every 15 minutes, and between Uxbridge and Aldgate every 15 minutes.
TfL said tickets are being accepted on London Buses and Chiltern Railways.