SYDNEY (BLOOMBERG) - Crown Resorts Ltd, the Australian casino company controlled by billionaire James Packer, plunged after the Chinese authorities detained 18 of its employees, including the head of its international high-roller operations.

The stock fell as much as 9.8 per cent in Sydney to A$11.68, headed for its biggest one-day decline in almost eight years.

Mr Jason O'Connor, head of Crown's VIP International team, is among those being questioned, the company said in an e-mailed statement. Crown hasn't been able to speak with the staff and is working with Australia's Foreign Ministry to make contact with the group, it said.

China's Foreign Ministry said in a statement that Australians had been detained for suspected involvement in gambling crimes, according to the Australian Financial Review. China's government said in February last year that the authorities were focusing on casino operators from neighbouring countries that have set up offices to attract Chinese citizens to gamble abroad.

More than one-third of Crown's revenue at its Australian resorts in Perth and Melbourne in the year ended June was generated by international visitors, predominantly from mainland China, Crown said in its latest annual report.

"Crown is staying in close contact with and is providing support to the families of our employees in China and Australia," the company said in the statement.

The company said it hasn't been "provided with details of why its employees have been detained".

Australia's Foreign Ministry is aware of reports of the possible detention of a number of Crown employees across China overnight on Oct 13 to Oct 14, including three Australians, it said in an e-mailed statement.

The Chinese authorities have three days in which to notify of the detention of Australians, according to the terms of a bilateral consular treaty, it said.