With the thieves having not been caught more than two days on from the heist, experts fear the jewellery will already be long gone.

Ms Beccuau said she hoped announcing the estimated worth of the jewellery would make the robbers think twice and not destroy them.

She added the thieves would not pocket the full windfall if they had "the very bad idea of melting down these jewels".

The items taken, previously described as having inestimable worth, include a diamond and emerald necklace Emperor Napoleon gave to his wife, a tiara worn by Empress Eugenie, the wife of Napoleon III, and several pieces previously owned by Queen Marie-Amelie.

Investigators found a damaged crown that used to belong to Empress Eugenie on the thieves' escape route - apparently having been dropped as they departed in haste.

Four masked thieves used a truck equipped with a mechanical lift to gain access to the Galerie d'Apollon (Gallery of Apollo) via a balcony close to the River Seine.

Two of them cut through a glass window on the first floor using a battery-powered disc cutter and entered the museum. They then threatened the guards inside, who evacuated the building.

The thieves had tried to set fire to their vehicle outside but were prevented by the intervention of a member of museum staff. They were seen making off on scooters.

French President Emmanuel Macron described the robbery as an attack on France's heritage.

Security measures have been tightened around the country's cultural institutions, after a preliminary report found one in three rooms in the Louvre lacked CCTV and that its wider alarm system did not go off.

Justice Minister Gérald Darmanin said security protocols had "failed", lamenting that the thieves being able to drive a modified truck up to the museum had left France with a "terrible image".

Authorities believe they are chasing a team of professionals, given how quick and organised they were.

Experts in art recovery previously told the BBC investigators had just one or two days to track down the items before they could be considered gone for good.

It is most likely they have been broken down into precious metals and gems, smuggled out of the country and sold for a fraction of their worth, other experts have said.

Louvre heist: Stolen jewellery worth €88m, prosecutor says