Billionaire casino magnate James Packer has expressed "deep concern" for the Crown Casino employees detained in China, amid reports authorities are preparing to press charges on alleged gambling crimes.

Three Australians are among the 18 sales and marketing executives who are detained in China.

The Crown staff are under investigation for violating strict laws that prohibit direct marketing of casinos to large groups in China, and could face up to 10 years' prison as China's anti-corruption crackdown hits the gaming industry.

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Sources close to the investigation are reportedly expecting charges for the Crown staff, who were detained five days ago.

Mr Packer, who is the largest Crown Resorts shareholder, said in a statement that while awaiting details from Chinese authorities he has asked Crown to do "everything possible" to contact the employees.

"I am respectful, that these detentions have occurred in another country and are therefore subject to their sovereign rules and investigative processes," he said.

"Crown will do whatever it can to support our employees and their families at this difficult time.

"Our number one priority is to be able to make contact and to ensure they are all safe."

Australian officials given access to detained staff

The Crown Resorts Board met last night to receive an update on the latest information provided by the Department of Foreign Affairs and Trade (DFAT), a spokesperson said in a Crown Resorts statement.

"The board was also provided with an update on the arrangements which were being made to make contact with the detained employees, and to support their families during this difficult time," the statement said.

Australian officials have been granted access to the Shanghai detention centre, where the three Australians are being held.

Prime Minister Malcolm Turnbull says they are being provided consular assistance.

"At any time there are several thousand Australians who are in trouble with the law in other jurisdictions and we provide support for them and assistance to them, that's part of our job," Mr Turnbull said.

Crown Resorts said it has organised local lawyers and briefed family members both in China and Australia.

Analysts say such arrests are not unprecedented for foreign casino operators in China, and foreigners are usually dealt with on a case-by-case basis.