Updated 12.30pm

Police in southern France on Wednesday detained a man who had broken into a museum overnight and threatened to turn it into a "hell", provoking a four-hour standoff, authorities said.

A search was still on for a possible accomplice at the archaeology museum in the Mediterranean town of Saint-Raphael, the government's top regional official said.

Officer's from the elite RAID crisis intervention unit as well as a bomb disposal squad had surrounded the site, where several messages in Arabic had been scrawled on the walls, including: "The museum is going to become a hell".

The man had refused to communicate with authorities. 

Police have not specified if he was armed or if other people were in the building.

Officials locked down a large part of the historic centre of the resort town of some 35,000 people, tucked between Cannes and Saint-Tropez.

"There are barricades everywhere, the street is completely blocked off," Sebastian Belkacem, who owns the Duplex restaurant opposite the museum, told AFP by telephone.

"We were in our apartment, above the restaurant, when the police woke us up and asked us to evacuate," he said. "But we are holing up here, and waiting."

The government's main regional official, along with the local prosecutor and the mayor of Saint-Raphael, were expected to hold a press conference later Wednesday.

The museum, a historic monument, includes a medieval stone church and a vast collection of amphoras and other items from the region's Roman history.