A spokesman for Southern said: “The 17.46 service from London Victoria to Littlehampton was terminated at Haywards Heath after a suspicious item was found on board.
“Police were called to the scene as a precaution and later found the item was not suspicious and the scene was safe.
“Reports of the item were received by Southern at 6.55pm and a decision was taken to terminate the service.
“The scene was declared safe at 7.33pm.”
Platforms 1 and 2 at Haywards Heath were closed as police investigated, according to Southern, but have now been reopened.
Southern expects the travel disruption to continue until the end of today’s service.
The Littlehampton-bound service had been delayed leaving London Victoria by 15 minutes due to a passenger being taken ill on a previous service, according to Southern.