A London Underground line was temporarily closed after contractors drilled a hole in the tunnel roof.
Transport for London (TfL) said it halted services on the Central Line between White City and Marble Arch because concrete debris fell on to the track.
Operations director Peter McNaught said: "The Central Line was part-suspended this evening due to an obstruction on the track in the Shepherd's Bush area, caused by external contractors involved in building work in the local area.
"Our engineers worked hard to clear the debris as quickly as possible and ensure the line was safe to reopen to passengers. We will be carrying out a full investigation into the cause of this issue alongside those involved."
The line reopened at around 8.45pm after being closed for a couple of hours, but severe delays continued on the east-west line which links Ruislip and Ealing in the west with Epping in Essex via central London.