Officials said the hold-up took place in the morning at a jewellery exhibition at the Carlton Hotel.
The hotel is located on the Croisette promenade, one of the most prestigious locations in the city.
BBC said the Carlton Hotel is where Alfred Hitchcock's 1955 film "To Catch A Thief" -- about a jewel thief -- was filmed.
An exhibition of diamonds was being held in the hotel's lobby.
Media reports said the robber made off with the jewels in a briefcase.
Police said an operation was underway to catch the culprit and recover the jewels.
The Cannes film festival was hit by two jewellery thefts in May.
A necklace by a Swiss jeweller said to be worth 1.9 million euros (USD 2.5 million) was lost after a party at a five-star hotel in the resort town of Cap d'Antibes, while more than 777,000 euros (or USD 1 million) worth of jewels were taken from the hotel room of an employee of another Swiss jeweller.
--IANS (Posted on 28-07-2013)