The deputy chairman of Sotheby’ Asia and International Head and Chairman of Chinese Works of Art, Nicolas Chow, presents the Seal of the Mandate of Heaven used by Emperor Kangxi during an auction preview at Sotheby's in Hong Kong, China on 14 March 2016. [Photo: Imagine China]

The largest imperial seal used by Emperor Kangxi has been auctioned in Hong Kong for around 12 million US dollars.

Sotheby's hasn't said who purchased the seal, other than to say the buyer is from Asia.

Sotheby's Nicolas Chow says the 12-million US dollar purchase is the 3rd highest price ever paid for a Chinese imperial seal sold at an auction.

"These objects are very, very hard to price, because you're not really selling the physical object as it is, you're not selling a piece of wood, you're selling the symbolism of the seal. So it's always very hard to gauge how much it will fetch. $12 million is an extraordinarily strong price for an object like that."

Imperial seals were pieces of wood engraved with the Emperor's name and title, and were used to mark official documents issued by the court.

Kangxi ruled China for 61-years from 1661 to 1722, making him the longest-ruling Emperor in Chinese history.