Thieves broke into Paris' Louvre museum through a window on Sunday, stealing "priceless" items of jewellery before escaping on motorbikes, the French government said.
The thieves struck at about 9.30am (0730 GMT) when the museum had already opened its doors to the public, and entered the Galerie d'Apollon building, which is home to the French Crown Jewels, the Interior Ministry said in a statement.
It did not say exactly what had been taken.
"The investigation has begun, and a detailed list of the stolen items is being compiled. Beyond their market value, these items have priceless heritage and historical value," the statement said.
No injuries were reported, either among the public or among Louvre staff or law enforcement officers, it added.
The Louvre, the world's most-visited museum and home to Leonardo da Vinci's Mona Lisa, said on X it would remain closed for the day for "exceptional reasons".
Earlier this year, officials at the Louvre requested urgent help from the French government to restore and renovate the museum's ageing exhibition halls and better protect its countless works of art.
Last year, the Louvre welcomed 8.7 million visitors.
