An 18-year-old student working a summer job at a Belgian building site has stumbled across a hidden trove of gold worth an estimated €9 million (AUD $14 million).

“We suddenly saw something lying there,” 18-year-old Kobe told local news outlets.

 “At first I thought it was €1 coins. So we started digging them up. Then we saw a gold bar. It turned out to be a bit more than we thought.”

The student was working with colleagues on the site of a former brewery, excavating the trenches for a sewage system just 30km north-west of Brussels, when they made the discovery on Tuesday.

The hoard was stashed in a bag in a bricked-in cellar wall beneath the grand villa built for the brewery’s original owner, Theophilus Van Assche, and included gold coins, nuggets, and numbered bullion bars.

“It’s just not something you expect when you’re working on a regular Tuesday morning,” Kobe said, “It was really bricked in there – not in a safe or anything.”

The brewery closed in 1970, with the property being renovated by the social welfare organisation CAW Oost-Vlaanderen  to create new offices and housing.

“The Brouwershuis was a beautiful building, but it is being completely gutted,” a representative for the welfare organisation said.

“Ultimately, only the walls will remain. Labourers were laying drainage pipes when they stumbled across the gold.”

The treasure has since been transferred to a secure facility in Brussels as an official investigation will be launched to determine its legal ownership.

Authorities must first verify that the bullion was not stolen property or the proceeds of criminal activity.

A former mayor said that the fortune had “certainly stayed in the family. It wouldn’t surprise me at all if they had decided to put at least some of it in gold, and then to hide it in a safe place.”

Kobe said he and his colleagues knew that they had to report the find.

 “If it had been a few coins, maybe not,” he said. “But maybe we’ll get some kind of finder’s reward eventually.”

Image: Facebook/Dendermonde Local Police