GENEVA - Huge diamonds and gems with royal cachet are expected to fetch strong prices next week as buyers chase unique pieces in a revived international jewelry market, rival auction houses said on Friday.

The semi-annual sales in Geneva, Europe's capital for jewels on the block, follow highly successful results in both Hong Kong and New York, according to Christie's and Sotheby's.

Collectors from Asia, especially China, and the Middle East are increasingly bidding for top-quality gems in the Swiss city alongside traditional buyers from Europe and the United States.

"The market now seems to have returned in great strength. Last year was one of our best years," David Bennett, chairman of Sotheby's Europe and Middle East jewelry department, told Reuters in an interview.

Sotheby's, which had record sales in Hong Kong last month, expects to net 35 million Swiss francs ($32.77 million) at its jewelry and watch sales in Geneva.

"The vast majority of the sale comes from private owners. Virtually all the noble section has never been on the market before. The jewels are fresh and quality is very high," he said.

"Period jewelry, collection jewelry and noble jewelry are getting scarcer and scarcer. Competition is growing and estimates are being exceeded quite comfortably. Also for fine diamonds and colored stones," Bennett added.

Jean-Marc Lunel, head of Christie's jewelry department in Switzerland, said buyers are paying top prices for high-quality diamonds, colored gem stones and jewels of special provenance.

"Colored diamonds take the direction of Hong Kong. In Geneva, we are focusing on fine quality, signed pieces from French master jewelers," he told Reuters, pointing to pieces by Cartier, Van Cleef & Arpels, Boivin and Chaumet.

CHINESE ACTIVE BIDDERS

As Chinese buyers now take home roughly 20 percent of its jewelry, privately held Christie's has moved Brenda Kang, a Chinese-born Singaporean expert, to its Geneva offices.

"The Chinese are very, very active in the jewelry field. They have a lot of interest but are not always successful, they are also under-bidders. But they are bidding actively and fiercely in all our jewelry auctions," Lunel said.

Christie's estimates that its Wednesday night sale will fetch between 23 million and 33 million Swiss francs.

Its star lot is a flawless rectangular-cut white diamond weighing 40.21 carats, estimated at $4.5 million to $5.5 million. A stunning necklace set with 20 round diamonds, known as a riviere, could go for $1.8 million to $2.4 million.

Christie's also offers a diamond and enamel brooch designed by award-winning British jeweler Shaun Leane, who named it "White Light" after being inspired by a Dylan Thomas poem about the first snow of winter.

"It is an extraordinary jewel, a modern contemporary creation and of course a unique piece," Lunel said of the brooch, estimated at $1 million - $1.5 million and whose cascading diamonds weigh a total of nearly 41 carats.

Star lots at Sotheby's sale on Tuesday are an emerald-cut white diamond of 52.82 carats and a ring by French jeweler 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.

The large white diamond is type IIa -- the top grading for both polish and symmetry, meaning it is the most pure.

"It's a new stone, therefore the buyer has the possibility of naming it," Bennett said of stone, estimated to fetch $7 million.