A fault with the signalling system on the railway line between Brighton and Haywards Heath is causing disruption this morning.
National Rail said train services running to and from these stations may be delayed by up to ten minutes.
A spokesman said: “Services from Brighton travelling towards Haywards Heath will experience delays as they travel between Preston Park and Hassocks.
“There is a fault with the signalling system situated in the tunnel between Preston Park and Hassocks.
“Whilst ongoing, services will need to run at a reduced speed through the affected area.
“Network Rail technicians are investigating this fault and are working to repair it as soon as possible.”
Passenger can check their journey using the National Rail Enquiries real-time Journey Planner.