Dunedin Railways operation manager said Grant Craig said there was ''unauthorised access'' to a Dunedin Railways carriage.
When staff came to work yesterday a carriage was open.
There was no sign of forced entry but it appeared the carriage was used for a ''party''.
''There was no damage - it was more of a mess.''
A few empty wine bottles remained and paper towels from the carriage's toilet had been shredded into small pieces.
Someone had attempted to set a fire with some paper but had been unsuccessful.
''It didn't take,'' Mr Craig said.
He had not discounted it being an attempted arson.
The toilet had been used and paper was inside the bowl.
The toilet had not been flushed, as the flush mechanism could not be activated unless the train was moving, he said.
The carriage was not commissioned for any trips yesterday but it would be ready to take passengers to the Port Chalmers Seafood Festival today.
Senior Sergeant Brian Benn, of Dunedin, said a forensic team investigated the incident yesterday and police inquiries were continuing.
