The incident happened after what was due to be Wednesday's 0940 GMT service from Brighton to West Worthing was cancelled due to a suspected fault.

South Central Trains staff thought the train had been emptied and it was taken to sidings near the station, when it was realised some passengers had not got off.

The train was being taken back to the station so they could get off when it came off the rails.

South Central said nobody had been injured in the incident, but said it was holding a joint investigation with Network Rail to try to find out how it had happened.

The rail firm warned the derailment would lead to delays to services around lunchtime.