All Southern Rail journeys along that line have been scrapped due to lack of signalling staff.
Commuters are advised to use Stagecoach buses instead as a rail replacement bus is not yet ready.
In a tweet Southern Rail said: ‘We've been advised of signalling staff being unavailable at Chichester signalling box.
‘You're advised to delay travelling until later if you can.
‘If you have to travel now, you'll need to use an alternative route to complete your journey.
‘You can use your ticket on: Stagecoach 700 between Havant, Chichester, Bognor Regis and Brighton.
‘South Western Railway between Portsmouth/Southampton, Havant and London Waterloo.
‘If you are using an alternative route, your journey time will be extended by up to 45 minutes.
‘The following services will be changed by the incident: Trains that usually run between Brighton and Chichester will now run between Brighton and Littlehampton.
‘Trains that run between Brighton and Portsmouth and Southsea will be cancelled.
‘Trains that usually run between Littlehampton and Portsmouth will now run between Littlehampton and Bognor Regis.
‘Trains that usually run between London Victoria and Portsmouth/Southampton will now run between London Victoria and Bognor Regis.
‘Network Rail have advised that they expect a signaller to be available from approximately 8am.’
Passengers can plan an alternative bus route on the Stagecoach website at stagecoachbus.com/plan-a-journey.