They helped themselves to chalices and other treasures, much of it gold, at the cathedral in Oloron-Sainte-Marie, near the Spanish border.

It is the first time the cathedral, which dates back to the 12th Century, has been attacked.

Oloron-Sainte-Marie was listed as a Unesco World Heritage site in 1998.

Chalices were stolen

The Bishop of Bayonne and Oloron, Marc Aillet, called the theft sacrilegious.

The burglary happened at 02:00, council officials confirmed. The gang made their escape in another vehicle, according to witnesses.

The burglary has shocked the townspeople who are now making an inventory of the treasures and relics

Situated some 50km (31 miles) from the border, the cathedral is a popular stop-over for Catholic pilgrims heading to Spain's Cathedral of Santiago de Compostela.

"Over and above the monetary value, residents now find themselves cut off from their history and their heritage," a town official told AFP news agency.

Police have launched an investigation.