A rare grey pearl necklace that once belonged to a British aristocrat sold for HK$41 million ($5.27 million) in Hong Kong on Wednesday, auctioneers Sotheby's said.

The string of pearls was part of the collection of Viscountess Cowdray, Lady Pearson.

The buyer, a private collector from Hong Kong, made the winning bid by phone.

Viscountess Cowdray, who died in 1932, was famed for her collection of furniture and works of art, as well as jewellery. The pearls were first put up for auction in 1937.

In 2012 the same necklace was sold for $3.35 million at Christie's in London.

Also on Wednesday a 27.68-carat Kashmir sapphire and diamond ring, dubbed "The Jewel of Kashmir", was sold for HK$52.28 million, once again to a Hong Kong collector.

A portrait of a consort of the Qing Dynasty emperor Qianlong was sold for HK$137.4 million to an anonymous buyer, setting a record for a Chinese imperial portrait.

The painting is thought to be a 18th century piece by court artist Giuseppe Castiglione.