Shares in billionaire James Packer's Crown Resorts plunged Monday after 18 sales and marketing staff were detained in China, including an executive in charge of luring high-rollers to Australia.

The gaming company's stock fell 13.9 percent to close in Sydney at Aus$11.15.

It followed news that three Australians were among those hauled in for questioning by Chinese authorities on Thursday and Friday last week, with the company unable to contact them.

"In relation to media reports on the weekend, Crown Resorts Limited believes that Crown's executive vice president VIP International, Jason O'Connor, is one of 18 Crown employees that have been detained by Chinese authorities," the company said in a statement Monday.

"To date, Crown has not been able to speak with its employees and is working closely with the Department of Foreign Affairs and Trade to urgently make contact with and ascertain the welfare of its employees.

"Crown is yet to be provided with details of why its employees have been detained."

China's foreign ministry said in a statement to AFP that Australian nationals had been "criminally detained by Chinese authorities for suspected gambling offences". 

"The case is under investigation," it added.

The Australian Broadcasting Corporation said it understood they were seized over soliciting Chinese high-rollers to gamble in overseas casinos.

The Australian Financial Review reported they may have been targeted as part of "Operation Chain Break", aimed at stopping the illicit flow of funds into foreign casinos.

Gaming companies are not allowed to explicitly advertise gambling in China.

The newspaper said police raided houses in Shanghai, Beijing, Guangzhou and Chengdu.

Australian Foreign Minister Julie Bishop said the government had been notified of the detention in Shanghai of three Australians among a number of Crown employees held across China.

Consular officials were making "arrangements to visit the Australians to offer appropriate assistance, all of whom have legal representation provided by their employer", Bishop said in a statement. 

"The Australian Government is also providing consular support and information to the families in Australia, in consultation with Crown."

Crown operates casinos across Australia and the world, including in Macau, where revenues have been hit hard by a Chinese corruption crackdown which has driven away many big-spenders.

Macau gaming companies listed in Hong Kong's stock exchange also tumbled on the news, with Sands Macau and Galaxy Entertainment more than three percent down Monday.

Graft has become endemic in China and President Xi Jinping launched a much-publicised anti-corruption drive after he came to power in 2012.

Packer, who is engaged to pop diva Mariah Carey, owns 53 percent of Crown Resorts but resigned as chairman in 2015.

Sourc: AFP