A Polish official says ground-penetrating radar images have left him "99% convinced" that a World War Two German military train is buried near the south-western city of Walbrzych.
Deputy Culture Minister Piotr Zuchowski said images appeared to show a train equipped with gun turrets.
Local legend says a Nazi train filled with gold, gems and guns went missing near the city in 1945.
Mr Zuchowski called the latest evidence an "exceptional" discovery.
He did not reveal the location of the find but said he personally hoped that it would bring to light looted art and Nazi archives.
However, he also reiterated warnings to treasure hunters that it may be booby-trapped.
Mr Zuchowski said information about the train had apparently come in a deathbed confession from a person involved in concealing it.
Earlier this month, a Pole and a German told authorities in Walbrzych that they knew the location of the armoured train.
Through lawyers, they said that they wanted 10% of the value of anything that was found.
The BBC's Adam Easton in Warsaw says no documents have ever been discovered confirming the existence of the train but, between 1943 and 1945, Germany forced prisoners of war to dig more than 9km (five miles) of underground tunnels near Walbrzych that were apparently to be used as factories.
Some are now tourist attractions.
Walbrzych's deputy mayor told reporters on Wednesday that the train's location was being kept under wraps, along with the identity of the two men who claimed to have found it.
"The find is within our administrative boundaries," said Zygmunt Nowaczyk.
"I cannot of course reveal the exact place."
The train was rumoured to have been carrying gold from what is now the Polish city of Wroclaw as the Soviet army closed in at the end of World War Two.
Local folklore said it went missing near Ksiaz castle, 3km (two miles) from Walbrzych.
In a statement earlier this week, Mr Zuchowski warned the public to stop searching for the train until official procedures to secure the find were completed.
He said there could be "hazardous substances" and there was a "huge probability that the train is booby-trapped".