WALBRZYCH, Poland — Two treasure hunters who were hoping to find a buried Nazi train full of gold, jewels and weapons halted their efforts on Wednesday, after a week of digging turned up no sign of the train.

The excavation began last week outside the town of Walbrzych, Poland, in an area that was part of Germany before World War II. The dig became the subject of intense interest after the treasure hunters claimed last year that they had found what appeared to be a buried rail tunnel that might contain such a train.

According to local lore, the train vanished after it entered a complex of secret tunnels carved by the Germans into the Owl Mountains as they fled the advancing Soviet Army in 1945. But skeptics have said there was no hard evidence to corroborate the story, and the digging near Walbrzych did not change that.

“Unfortunately, the excavation has revealed no train, no tunnel and no trackway in the location where we thought they would be,” Andrzej Gaik, a spokesman for the project, said Wednesday in a telephone interview.

The treasure hunters, Piotr Koper and Andreas Richter, said in an interview that ground-penetrating radar images had seemed to show a regular rounded shape about 16 feet underground that looked like a tunnel ceiling.

It turned out to be of natural origin, according to Tomasz Siwiec, the coordinator of the project. “It was an iceberg that formed this beautiful dome of loam that we thought, by looking at the radar images, to be the tunnel,” Mr. Siwiec said. “You may say that the iceberg played a joke on us.”

Mr. Gaik said that the explorers were disappointed but not discouraged, and that they would try again in September, using drills rather than excavators and bulldozers, to see if they can find the tunnel they hope is nearby.

The intense speculation about the elusive train brought global attention to Walbrzych, a charming if slightly run-down town of 120,000 people that has struggled with high unemployment since five coal mines in the area closed in the 1990s.

Local officials expressed doubts about the excavation project from the beginning, and declined to contribute public funds to the search. But they allowed it to go ahead, and many hopeful local residents actively supported the explorers.

Mr. Richter said in an interview last week that most of the 64 people who were working on the project were volunteers, and that the heavy equipment was donated.

Arleta Adamska, 58, who runs an inn near the excavation site along with her husband, said she had been cooking free meals for the searchers.

“I am 100 percent certain they will find something sooner or later,” she said. “If not here, then in another place. Walbrzych is full of mysteries. But we are already benefiting: We have been booked up all summer.”

Arkadiusz Grudzien, the spokesman for the mayor of Walbrzych and head of the City Promotion Office, said in an interview that tourism in the town was up 44 percent from the previous year.

“The publicity the town has gotten in the global media is worth roughly around $200 million,” he said. “Our annual budget for promotion is $380,000, so think about that. Whether the explorers find anything or not, that gold train has already arrived.”

The mayor, Roman Szelemej, noted in an interview on Friday that before the hunt for the Nazi train began, Walbrzych was known mainly for illegal coal mining.

“I’m thinking of naming a roundabout after Koper and Richter,” Mr. Szelemej said, “in thanks for their services to our town.”