A mysterious man with a shotgun forced trains to be suspended on the Cranbourne-Pakenham line on Tuesday night.

Witnesses reported seeing a man with a shotgun in a park off Arthur Street, Hughesdale, in Melbourne's south-east.

Police searched the area and found shell casings in the park, but no sign of the man.

Amid fears the man could still be armed and roaming the area, police requested that all trains around Hughesdale be stopped at 6.51pm.

Train services were suspended for an hour, before police gave Metro Trains the all clear at 7.51pm.