A Chinese Khotan-green jade seal carved in 1796 to commemorate the end of the Qianlong emperor's reign is to sell at Sotheby's.

It carries an estimate of $10m-15m ahead of the Dragon Emperor auction in Hong Kong on October 5.

Khotan jade was mined on China's western borders

Focusing on treasures from the Qianlong period (1711-1799), it's one of six Chinese Works of Art Autumn Sales that Sotheby's plans to hold that day.

The lot is one of 20 replicas of the enormous original seal, which Qianlong had carved for his son and heir the Jiaqing Emperor.

Qianlong wrote: "After I have passed on the throne, I shall have the phrase 'Taishang Huangdi zhi Bao [Treasure of the Emperor Emeritus]' carved onto my best jade seal… to display the flourish and growth of the dynasty while I am the Emperor Supreme."

The original, which measures over 20cm across, was made in 1795 and is now one of the centrepieces of the Beijing Palace Museum.

The present example measures 12cm across, making it the second largest of all the replicas.

Unlike the original, it was actually used by the Qianlong emperor in the last days of his reign.

Smaller specimens have sold in the past, with one carved from Khotan-green jade achieving $2.1m at Sotheby's in 2009.

A seal made for the Kangxi emperor made $11.4m earlier this year.

Please sign up to our free newsletter to receive exciting news about antique auctions.