Hundreds of pro-democracy activists have gathered in Australian cities in support of protesters in Hong Kong in recent weeks.

However, there have been a number of scuffles between the pro-democracy and pro-China groups.

A Chinese foreign ministry spokesman said it was "totally understandable and reasonable" for Chinese students and other Chinese citizens overseas to "express indignation and opposition against such words and deeds that attempt to separate China and smear its image".

"We also hope overseas Chinese can express their patriotism in a rational way and protect themselves from harm."

The official said overseas Chinese should observe local laws and regulations.

"In the meantime, we hope relevant countries can understand and respect their legal activities and protect their lawful rights and interests."

Hong Kong has been plunged into its biggest political crisis since the former British colony's return to Chinese rule in 1997, with a wave of protests against a now-suspended extradition bill which would see people sent to mainland China for trial in Communist Party-controlled courts.

The protests, which started in April, have now transformed into broader demands including the resignation of Hong Kong's embattled leader Carrie Lam and calls for a "free Hong Kong".

Meanwhile, a poster with a death threat on it aimed at pro-Hong Kong protesters has been removed from a wall at the University of Technology Sydney.

The poster showed a drawing of a person holding another person over a cliff with the caption: "Take back your Hong Kong independence speech if you don't want to die".

A spokesman for the university told AAP the posters on the wall were reviewed regularly, but the wall had been made available to students earlier this month as a way of peacefully expressing their views.

The wall is overseen by campus security.

Australian Associated Press