Dealers stand at sic bo tables inside the Galaxy Macau Phase 2 casino, developed by Galaxy Entertainment Group Ltd., in Macau, China, on Tuesday, May 26, 2015. [Photo: CFP]

Australia's Department of Foreign Affairs and Trade issued a statement saying they are looking into a case where 18 employees from Melbourne-based gambling firm Crown Resorts were reportedly arrested in China on Thursday.

China is required to inform Australia if they have detained one of its nationals within 72 hours.

Fairfax Media reported three top Australian executives are among the detained, including Jason O'Connor, Crown Resorts' executive general manager in charge of international VIP services.

Crown Resorts' spokeswoman declined to provide further details about the case, when being reached by Fairfax Media.

A BBC report said it still remains unknown on whether any charges had been laid.

Gambling is considered illegal in the Chinese mainland, while Macau remains as the only city in the country that can operate casinos and other gambling-related business.

But Fairfax said many casino operators from overseas are trying to sidestep the ban by promoting their resorts and cities instead.