Updated

Up to 70 major artifacts were stolen from Greece's Ancient Olympia Museum in a brazen robbery Friday.

Two thieves used hammers to smash their way into the museum about 7.30am local time. They bound and gagged a female employee on duty before stealing the artifacts, according to Greek newspaper Kathimerini.

Greece's culture minister Paul Geroulanos tendered his resignation over the incident.

Experts are now assessing the damage to the museum and trying to work out precisely how many items have been stolen.

The museum is located next to the site where the ancient Olympics were held, and holds valuable artifacts related to the games.

It is the second museum in Olympia, holding mainly bronze and ceramic objects used by ancient athletes in the Olympics. The city's first museum is better guarded, and features statures and other architectural objects.

Friday's heist follows the theft of a painting by Pablo Picasso from Greece's National Gallery in Athens on Jan. 10.

The painting was "Woman's Head," a 1939 Picasso oil on canvas. The artwork was among three valuable works stolen from the gallery.

"Mill," a 1905 oil painting of a windmill by Dutch abstract artist Piet Mondrian, was also stolen, along with a sketch of St. Diego de Alcala by 16th century Italian artist Guglielmo Caccia, better known as Moncalvo, police said at the time.

The thefts come with debt-hit Greece locked in a deep recession amid fears over its future in the eurozone, with unemployment and social disorder on the rise.