Hong Kong: Prime Minister Malcolm Turnbull has accused North Korea of being one of the world's most "cunning, sophisticated criminals," involved in many serious crimes, including drug trafficking, in his strongest condemnation yet of the dictator Kim Jong-un.

And Mr Turnbull told US president Donald Trump and China's president Xi Jinping during a leaders' retreat in Vietnam that their relationship is one of the "single most priorities for the world today," urging them work together to pressure North Korea over is nuclear weapons program.

"If they can see eye to eye and cooperate on North Korea, for example, that problem, that regime, will be brought back to its senses," he said.

Speaking in Hong Kong where he urged financial regulators to crack down on North Korea's financial dealings in the port city, Mr Turnbull said North Korea should be seen as a criminal operation operating under the guise of a state.