Around £88 million worth of diamonds and jewels owned by an Israeli billionaire has been stolen from a Cannes exhibition in the most expensive heist in history.

The masked gunman held up the Intercontinental Carlton Hotel in broad daylight on Sunday while he filled a briefcase with items belonging to Russian-born Lev Leviev.

Mr Leviev’s company, Leviev, had allowed its precious merchandise to be used in a temporary exhibition in the French Riviera resort.

Philippe Vique, a deputy prosecutor in nearby Grasse, supplied the figure for the stolen goods, which is more than twice the initial estimate and comes after a thorough inventory check.

A local police officer told the Nice Matin newspaper: “The raid took place in broad daylight at a time when hundreds of tourists were enjoying the sunshine.

“It could not have been more daring. The thief took advantage of the crowds and the fact it was Sunday and the atmosphere was relaxed.”

Although the thief had made threats, police at the scene stated that “It was all over very quickly. There was no violence.”

The culprit allegedly gained access through a glass door that was accidentally left open.

A company spokesperson denied this report, stating that though the theft was frustrating, security was sufficient at the event.

Leviev also said they were “relieved that no one was injured in the robbery.”

An investigating officer assured the public that “a full and urgent operation is under way to catch the culprit and recover these jewels.”

Mr Leviev, a businessman and philanthropist, recently moved into a new £35 million house in Hampstead with his wife and nine children.