Australian authorities are clamping down on wealthy foreigners illegally buying real estate, ordering a Chinese billionaire to sell a Sydney mansion he recently bought for $30 million, a minister said yesterday. The billionaire, Hui Ka Yan, 56, is chairman of Hong Kong-listed real estate developer Evergrande Real Estate Group, which is based in Guangzhou, China. He is listed by Forbes as China's 15 wealthiest person with a fortune of $6.4 billion. The government on Tuesday ordered Evergrande subsidiary Golden Fast Foods to sell a Sydney Habor-front mansion known as Villa del Mare within 90 days. The company bought the Mediterranean-style property in the exclusive Potts Point suburb in November. The government said the acquisition was illegal because Golden Fast Foods, which is owned by Evergrande through a series of shelf companies in Australia, Hong Kong and the British Virgin islands, did not inform the Foreign Investment Review Board it intended to buy it.