A Hong Kong billionaire has spent a staggering $AU67.8 million on a 12.03-carat diamond for his seven-year-old daughter.

Property tycoon Joseph Lau bought the rock dubbed “Blue Moon” at an auction in Geneva, renaming it “The Blue Moon of Josephine” after his daughter.

The big buy came just a day after he spent $US28.5 million on a rare 16.08-carat pink diamond — the largest of its kind ever to be sold — which he promptly renamed “Sweet Josephine”.

The sale of the diamond formerly known as ‘Blue Moon’ broke several records.

It is now the most expensive diamond, regardless of colour, and the most expensive jewel ever sold at auction, experts say.

It also reached the highest-ever price per carat.

The previous world record for a jewel at auction was from the sale of the 24.78-carat “Graff Pink” diamond, which was sold by Sotheby's for $US46.2 million in November 2010.

The Blue Moon was discovered last year in South Africa, and its huge auction value shows the market for coloured diamonds continues to grow, auctioneers say.

Mr Lau has made similarly big headlines for other reasons lately, especially after he was found guilty last year of bribery in Macau.

He bribed a former minister in the famous gambling enclave in a bid to purchase prime development land.

But Mr Lau is unlikely serve time, as the semi-autonomous Chinese city does not have an extradition agreement with others.