Overrunning engineering works at London Waterloo station have caused travel delays for commuters returning to work after the bank holiday weekend.
Cancellations and delays to South Western trains during morning rush hour are expected to carry on until midday, National Rail warned passengers.
The station, London's busiest, has been expected to be fully functioning after weeks of major upgrade work.
"An issue arose this morning with complex signalling equipment being tested and the project team required more time to finish this work. The work has been completed and the site has been handed back into use," customers were told.
In addition, trains re-routed to Waterloo from across the south east due to the closure of London Bridge, Waterloo East and Charing Cross stations have been redirected to Blackfriars instead.
Commuters usually travelling into the shut stations have been warned that it will be busy and to take different routes and allow more time to travel.