A law firm in south-west Poland says it has been contacted by two men who have discovered the armoured train.
Polish media say the men want 10% of the value of the train`s contents.
Local news websites said the apparent find matched reports in local folklore of a train carrying gold and gems that went missing at the end of World War Two near Ksiaz castle.
The claim was made to a law office in Walbrzych, 3km (2 miles) from Ksiaz castle.
"Lawyers, the army, the police and the fire brigade are dealing with this," Marika Tokarska, an official at the Walbrzych district council, told Reuters.
"The area has never been excavated before and we don`t know what we might find."
Two news websites in Walbrzych said the train that was found had guns on turrets along its side. One website, walbrzych24.com, said (in Polish) that one of the men was Polish and the other German.
They were liaising with officials in the city, who have since formed an emergency committee led by the mayor to investigate the claims, the website says.
Another site, Wiadomosci Walbrzyskie, said (in Polish) the train was 150m long and may have up to 300 tonnes of gold on board.
Joanna Lamparska, a historian who focuses on the Walbrzych area, told Radio Wroclaw the train was rumoured to have disappeared into a tunnel, and that it had gold and "hazardous materials" on board.
Previous searches for the train in the same area had proved fruitless, Radio Wroclaw said.
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