Huge flawless diamonds and pieces by Cartier, Bulgari and other big-name jewellers sold for several times estimated prices at a Sotheby's sale in Geneva, the auctioneer said.

The semi-annual sale netted 60 million Swiss francs ($54.10 million), nearly double the low end of its pre-sale estimate.

'There were very, very strong prices for high-quality jewels. A mix of period pieces, jewels of royal provenance and spectacular gems all found new owners, many times exceeding the estimate,' David Bennett, chairman of Sotheby's Europe and Middle East jewellery department, told Reuters.

Some 50 per cent of lots sold for above their estimate, he said. 'It's a tremendous result.'

Top lot was a blue cushion-shaped diamond weighing 7.64 carats, mounted in a yellow gold and platinum ring, which went for a whopping 8.93 million francs to an anonymous buyer who paid double the pre-sale estimate.

'This is a world record per carat for a fancy, intense blue diamond at auction,' Bennett told a packed salesroom as he brought down the hammer to applause.

A white emerald-cut diamond weighing 52.82 carats, which he called 'one of the most beautiful stones to come to auction for several years', fetched 8.8 million francs after hectic bidding.

It went to a US jewellery dealer, according to Sotheby's, whose pre-sale estimate was just over 7 million francs for the flawless stone with top grading for polish and symmetry.

A stunning ring by Alexandre Reza mounted with a vivid blue diamond of 5.02 carats alongside a white diamond of the same pear-shape of 5.42 carats sold for 7.026 million francs to a private collector.

Bennett said it was a world record at auction for a piece designed by the French jeweller. Sotheby's pre-sale estimate was $4 million to $7 million.

'It is a sublime ring, the two stones are complementary and perfectly proportional. It's extraordinarily chic,' he said.

Several pieces belonging to Brazilian socialite Lily Marinho found new owners, including an emerald and diamond necklace and matching ear clips and ring which fetched 1.2 million francs, tripling its pre-sale estimate.

'Lily has often been photographed wearing it, to those living in Brazil it is very familiar,' Bennett said.

Raju Kothari, a Hong Kong-based jewellery dealer, told Reuters after the sale: 'I got four or five items. Prices are high but if you want to own rare things you have to pay.'

Rival Christie's has estimated it could fetch between 23 million and 33 million francs at its Wednesday night sale.

Its star lot is a flawless rectangular-cut white diamond of 40.21 carats, estimated at $4.5 million to $5.5 million. – Reuters