A carved imperial seal belonging to the Chinese emperor Kangxi is valued at up to $6.4m ahead of a sale at Sotheby's Hong Kong on April 6.

Kangxi ruled between 1661 and 1722 and is considered one of China's greatest rulers.

The Kangxi emperor's seal is carved from sandalwood and displays a mythical creature

Nicolas Chow, deputy chairman of Sotheby's Asia, explained: "This seal is emblematic of the Mandate of Heaven, which has legitimised the authority of rulers in China since the dawn of recorded history.

"This almighty principle was also the single guiding light for the Kangxi Emperor, China's longest reigning emperor, who is credited for completing the conquest of China, anchoring the Qing dynasty and ushering in a long period of great prosperity and peace.

"The Kangxi Emperor was the single most powerful person on earth at the time, ruling over a vast Kingdom and over 100 million subjects."

The reverse of the sandalwood seal reads "Jingtian Qinmin", which translates to "to respect heaven and diligently serve the people".

This was the central philosophy of the imperial Chinese system.

It's one of three seals to display these words. The other two (both carved from jade) were made in tribute by Kangxi's descendants, the Yongzheng and the Qianlong emperors.

The Qianlong emperor explained why he created his copy in a poem: "This one seal has been used by three generations and has yielded an unlimited amount of blessings on the realm.

"Why have I had its text carved again? It is because of its important meaning."

The present seal was housed at Xinuange (the West Warm Pavilion) towards the rear of Beijing's Forbidden City complex.

Sotheby's describes it as "the most important piece of Chinese history ever to come to auction".

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