A 10.10 carat vivid blue diamond is expected to set the record for the most expensive piece of jewellery sold at auction in Asia despite an ongoing growth slowdown in China's economy, Sotheby's said on Friday.

The "De Beers Millennium Jewel 4" is expected to fetch between $30mn and $35mn at the April 5 sale in Hong Kong, and is described by the auction house as the largest oval blue diamond ever to appear at auction and "internally flawless".

The diamond, which is slightly larger than an almond in size, came from South Africa's Cullinan Mine and was one of 12 displayed at London's Millennium Dome to mark the year 2000.

"There are no more than a dozen or so blue diamonds of fancy vivid colour and over 10 carats in the world, so they are very, very rare," Sotheby's Deputy Chairman for Asia Quek Chin Yeow told AFP.

The sale will come five months after the 12.03-carat "Blue Moon of Josephine" was bought for a record $48mn in Geneva by an Asian property tycoon - a further sign the jewellery auction market remains strong despite slowing Chinese growth.

The world's second-largest economy expanded 6.9% in 2015, the worst performance in a quarter of a century and a far cry from years of double-digit increases.

"Of course people are concerned about the China slowdown" Quek said, but added that sales of rare items seem to be largely unaffected by growth numbers.

"It's the rarity and the collectability of these wonderful objects. When they come to the market, they will have strong interest from all over the world," Quek said, adding that the location of the upcoming sale was a sign of confidence in the Asian market.

The previous record for a diamond sold in Hong Kong was set in 2013, with the sale of a 118-carat white diamond for $30.6mn.