Workers have made an unexpected discovery when demolishing an uninhabited house in France — 600 gold coins.

A paramilitary police officer said the workers discovered the coins in the cellar after rattling a mysterious, shell-shaped container.

They were Belgian, dated 1870, and bore the face of the then-reigning king of Belgium, Leopold II.

The gendarmerie said the treasure found in Brittany, a region in northwest France, has since been put under lock and key until they uncover more information about its origin.

Local media reports the hoard could be worth 100,000 euros ($117,861).

It’s not the first time French workers have stumbled across exactly 600 gold coins.

Back in 2014, three men found a secret booty in Normandy worth almost one million euros ($1.17 million). According to regional daily Paris Normandie, the jars contained six gold bars weighing one kilogram each and 600 gold coins, dating back from 1924 and 1927.

In this instance, for them it was “finders keepers” — but law caught up with them.

They were charged on charges of theft after tax officials noticed one of the men depositing high-value cheques.

Another golden discovery was also made in 2014 when German archaeologists recovered a find of over a million euros worth of Roman gold and silver jewellery from an amateur treasure hunter who dug it up illegally in a forest.

German media reported that the treasure hunter initially kept his discovery secret and was believed to have sold off part of it on the black market, but it was seized by the authorities when it came to their attention.

This story originally appeared in news.com.au.