At first sight, the man and three women who entered the Harry Winston store in Paris resembled the sophisticated international clientele who frequent this most exclusive of jewellers. But staff soon realised something was amiss – the women were really men in wigs and dresses and all four were holding guns.

They herded the 15 or so staff and customers into a corner – hitting some over the head – then loaded necklaces, brooches, watches and other valuables into their bags and made off with a haul valued at €85 million (£74 million). The biggest robbery in French history, and the second-biggest jewellery theft in Europe, took only 13 minutes.

French police, who arrived 15 minutes later, said that Harry Winston, the self-proclaimed king of diamonds and supplier to monarchs, aristocrats and film stars, had fallen victim to a highly professional and well informed gang.

The boutique, on the Avenue Montaigne in central Paris, was closed yesterday and three of the five window displays were empty. Members of France’s elite detective squad searched the premises for clues. They studied security camera footage and the alarm mechanism, which is linked to a centre in Switzerland. Witnesses told police that the robbers had spoken only French. Others said that they also spoke a second language but all agreed on the speed, efficiency and brutality of the criminals, who injured some of the staff, though they did not fire a shot.

The gang is reported to have known the names of some of the staff and the location of jewels hidden from public view, suggesting that they either had inside knowledge or had done extensive surveillance.

A police source said that the haul may already be heading for Eastern Europe, where it is likely to be sold at knockdown prices on the black market. “The former Eastern bloc is the new Eldorado for diamond traffickers,” the source said.

An insurance industry source said that the valuables would have to be dismantled before they could be sold, “considerably lowering” their value. The jewellery could not be sold intact without attracting attention, the source said.

A spokesman for Harry Winston said: “We are cooperating with the authorities in their investigation. Our first concern is the wellbeing of our employees.”

The business was founded by Jacob Winston in 1888 in New York before Harry, his son, transformed it into one of the world’s most celebrated jewellery chains. Its exclusive clientele has included the Queen, Diana, Princess of Wales, Sophia Loren and Marilyn Monroe.

Among Winston’s most famous gems are a 726-carat diamond bought by King Farouk of Egypt in 1951, a 69-carat diamond bought by Richard Burton for Elizabeth Taylor in 1969 and a 71-carat emerald acquired by Aristotle Onassis for Jackie Kennedy’s engagement ring in 1968.

The Avenue Montaigne store, off the Champs Élysées, is in the middle of the Parisian Golden Triangle. In October last year it fell victim to a heist when robbers stole jewellery worth €10 million. Despite a $500,000 reward, it was never found.

France’s biggest theft until this week occurred in 1992, when robbers got away with cash worth €31 million from a Bank of France branch in Toulon.

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