SHANGHAI (Reuters) - A Hong Kong buyer has paid US$32.6 million (S$40.76 million) for a near 10-Carat blue diamond at an auction held by Sotheby's in New York, underlining the rising demand for the sparkling gems from increasingly muscular Chinese buyers.

The unnamed Hong Kong collector saw off six other bidders to set a new record price-per-carat for any diamond, Sotheby's said in an announcement sent to Reuters on Friday. The price was around double pre-auction estimates.

China, the fastest growing diamond market, is driving global demand in the sector, with younger generations of Chinese increasingly choosing the precious stones over traditional gold baubles to mark engagements and marriage vows.

China's diamond jewellery sales grew 12 percent annually between 2008 and 2013, according to a report this year from diamond seller De Beers. It is now the second largest market behind the United States in the global US$79 billion sector.

The allure of China's diamond industry has tempted jewellers, miners and dealers alike, with players like De Beers, Tiffany & Co and Rio Tinto Plc's diamonds division eyeing the country to drive future growth.

Sotheby's is competing with rival auction house Christie's to attract Chinese buyers in Hong Kong and the mainland, who have become increasingly active in the wider global art market, helping drive up prices from jewellery to antiques.