The hotel in the sweltering French Riviera was hosting a temporary jewelry exhibit over the summer from the prestigious Leviev diamond house, which is owned by Israeli billionaire Lev Leviev.
A police spokesman said the theft took place around noon, but he could not confirm local media reports that the robber was a single gunman who stuffed a suitcase with the gems before making a swift exit. The spokesman spoke on condition of anonymity because he was not authorized to discuss the matter on the record.
Several police officers were placed in front of the Carlton exhibition room to prevent journalists and photographers gathered at the scene from entering.
A police officer stands on the balcony of the Carlton hotel in Cannes.
The luxury Carlton hotel is situated on the exclusive Promenade de la Croisette that stretches a mile and a half along the French Riviera, and is thronged by the rich and famous throughout the year. The hotel's position provides not only a beautiful view of the sea, but an easy get away for potential jewel thieves along the long stretch of road.
The valuable gems were supposed to be on public display until the end of August. It was not immediately clear how many pieces were stolen.
Hotel officials would not comment, and attempts to reach Leviev or his company were not immediately successful.
Several brazen jewelry thefts have taken place this year, including one in Belgium on Feb. 18 that involved some $50 million worth of diamonds.
The Carlton Intercontinental Hotel is a stable for Cannes Film Festival lovers.
In that heist, the stones from the global diamond center of Antwerp had been loaded on a plane headed to Zurich when robbers dressed in dark police clothing and hoods drove through a hole they'd cut in the Brussels Airport fence in two black cars with blue police lights flashing. They drove onto the tarmac, approached the plane, brandished machine guns, offloaded the diamonds, then left in an operation that took barely five minutes.
Authorities have since detained dozens of people and recovered much of the stolen treasure in that operation.
In May, Cannes was struck by two highly publicized jewelry heists during the Cannes Film Festival.
In the first theft, robbers stole about $1 million worth of jewels after ripping a safe from the wall of a hotel room. The jewelry was taken from the Novotel room of an employee of Chopard, the Swiss-based watch and jewelry maker that has loaned bling to A-list stars walking the red carpet at the film festival.
An exterior view of the Carlton Intercontinental Hotel in Cannes.
And in the second, thieves outsmarted 80 security guards in an exclusive hotel and made off with a De Grisogono necklace that creators say is worth $2.6 million.
Jewel thieves have been getting attention in Europe in more ways than one.
On Thursday, a member of the notorious "Pink Panther" jewel thief gang escaped from a Swiss prison after accomplices rammed a gate and overpowered guards with bursts from their AK-47s, police said.
Milan Poparic fled with fellow inmate Adrian Albrecht from the Orbe prison in the western state of Vaud.
Police say the Pink Panthers network's members are prime suspects in a series of daring thefts. According to Interpol, the group has targeted luxury watch and jewelry stores in Europe, the Middle East, Asia and the United States, netting more than €330 million since 1999.
Poparic is the third member of the Pink Panthers to escape from a Swiss prison in as many months, according to Vaud police.
