The men are demanding 10 percent of its value in exchange for revealing its location.
Historians say the existence of the train has never been conclusively proven, but authorities are not passing up this chance at possibly recovering treasures that locals and the government have sought for 70 years.
"We believe that a train has been found. We are taking this information seriously," Marika Tokarska, an official in the southwestern Polish district of Walbrzych, told The Associated Press on Thursday.
She said her office received two letters this month from a law firm representing the men, a Pole and a German who have chosen to remain anonymous, saying they are seeking 10 percent of the value of the train's contents for revealing its location.
The documents from the lawyers say the train is 150-meters (490-feet) long and loaded with guns, valuables and precious metals, but do not specify where it is. Authorities say they are willing to pay the reward if the information pans out.
A lawyer for the men, Jaroslaw Chmielewski, compared the find to the "wreck of the Titanic" in an interview on a local radio station.
Tokarska said that hiring a law firm gives a degree of credibility to the two men's claims, as do indications that they are familiar with the train's contents. But there are also reasons for caution: The first letter included some references to the area's topography that indicated they might not know the area very well.
Joanna Lamparska, an author who has written about the train and the region's history, says she believes it could be a scam.
"We have had a lot of stories like that in the last few years with people claiming they know where the train is," Lamparska told The AP. "But nothing was ever found."
Local stories say a German train left from the German city of Breslau (today the Polish city of Wroclaw) in April 1945 and headed westward toward Waldenburg (now Walbrzych.) At some point in the 60-kilometer (40-mile) journey it vanished.
During the war, Adolf Hitler had started creating a secret underground system in the area under the Owl Mountains, a project called "Riese," or "Giant." The region still belonged to Germany at the time and the project included seven separate tunnel systems. It was probably intended to be a military headquarters, though the project remains shrouded in mystery to this day.
Lamparska describes the area as one filled with meadows and mountains where the Nazis had secret rail lines and tunnels with camouflaged openings that went under the mountains.
The source of the train legend was a Polish miner who claimed he was told about it just after the war by German miners; he said they saw it being pushed into one of the tunnels. The miner has spent his life since trying to find the train, Lamparska said.
Already, the district governor has convened a meeting of firefighters, police, military and others to explore how they can safely handle the train if it is finally found. Not only could it be armed with explosives, but methane gas underground could add to the risk of an explosion.
The mystery is now compounded by questions about who the two men are.
"It could either be nonsense or they got the information directly from the Germans," local rescuer Krzysztof Szpalkowski told the private broadcaster TVN24. "Maybe one of these men is a descendant of people who took part in this action."