Commuters faced lengthy delays after a power surge caused the landslip detectors between Helensburgh and Thirroul to activate the alarms at 6.40am.

The alarm stopped trains from operating while staff checked for any landslides.‘‘To ensure the safety of our customers, passengers were held on board trains until it was safe to start operations again,” NSW Trains Link chief executive Rob Mason said.

‘‘Buses were organised to replace trains but customers were advised to delay their travel.’’