Watford commuters are facing severe delays on the trains this afternoon as service is suspended on the London Overground.
The interruption in service between Willesden Junction and Watford Junction is a result of a fault with the track at Hatch End.
Tickets are being accepted on London Buses and London Underground services.
Train operators do not expect the problem to be fixed before the end of the day.
Virgin Trains, London Midland and Southern services have not been affected.