Beijing: Foreign Affairs Minister Julie Bishop has confirmed the detention of a fourth Australian in China in connection with the nationwide blitz on Crown Resorts' activities on the Chinese mainland.

The fourth Australian is not a Crown employee but is being held along with the 18 staff detained on "gambling crimes" earlier this month, three of whom are Australian nationals.

"There are now four Australians involved, three are Crown employees and a fourth person we have learnt is not a Crown employee but is detained along with them," Ms Bishop told the ABC on Sunday.

She said it had taken time to negotiate consular access for some of the Australians detained because they held more than one passport.