HONG KONG: A digital artwork by humanoid robot Sophia was sold at auction on Thursday for $688,888 in the form of a Non-Fungible Token (NFT).

NFTs, a digital signature saved on blockchain ledgers that allows anyone to verify the ownership and authenticity of items, have become the latest investment craze, with one artwork selling this month for nearly $70 million.

Sophia, who was unveiled in 2016, produced her art in collaboration with 31-year-old Italian digital artist Andrea Bonaceto, known for colourful portraits, some of which depict famous people, such as Tesla's chief executive, Elon Musk.

The robot has combined elements from Bonaceto's works, art history and her own physical drawings or paintings on various surfaces multiple times in a process her creator David Hanson describes as "iterative loops of evolution."

Titled "Sophia Instantiation," the digital work is a 12-second MP4 file showing the evolution of Bonaceto's portrait into Sophia's digital painting, and is accompanied by a physical artwork, painted by Sophia on a printout of her self-portrait.