Anti-extradition bill protesters walk among tear gas as they attend a march in Hong Kong on Sunday. Reuters

Pro-democracy protesters in Hong Kong are set to defy Chinese authorities with another two major rallies later Sunday, a day after police fired tear gas to disperse them in one of the city's most renowned tourist districts.

Tsim Sha Tsui, a harbourside district known for its luxury malls and hotels, was filled with acrid plumes of tear gas on Saturday night as small groups of hardcore protesters battled police in streets usually brimming with tourists and shoppers.

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Semi-autonomous Hong Kong has seen two months of protests and clashes triggered by opposition to a planned extradition law that quickly evolved into a wider movement for democratic reforms.

Anti-extradition bill protesters gather during a march in Hong Kong on Saturday. Eloisa Lopez/Reuters

Authorities in Hong Kong and Beijing this week signalled a hardening stance. Dozens of protesters were charged with rioting and the Chinese military said it was ready to quell the "intolerable" unrest if requested.

But the largely leaderless protest movement remains unbowed.

Two simultaneous marches are planned for Sunday afternoon as well as a city-wide strike on Monday, making further clashes all but inevitable.

One of Sunday's marches will try to end in a park near the Liaison Office, the department that represents China's central government in the semi-autonomous hub.

Two weeks ago the office was pelted with eggs and paint in a move that infuriated Beijing and sparked the rapidly escalating warnings from the mainland.

Slingshots and tunnels

The last fortnight has seen a surge in violence on both sides with police repeatedly firing rubber bullets and tear gas to disperse increasingly hostile projectile-throwing crowds.

Police fire tear gas into a crowd in Wong Tai Sin district in Hong Kong on Saturday.

A mob of pro-government thugs also attacked demonstrators, putting 45 people in hospital, with many accusing the police of being too slow to respond.

This weekend has seen no let up in the violence.

In Tsim Sha Tsui masked demonstrators smashed the windows of cars in a police parking lot and daubed nearby walls with graffiti.

One team of protesters created a large slingshot -- held up by two members -- to launch bricks at the building.

Others put up barricades on busy shopping thoroughfares and temporarily blockaded a cross-harbour tunnel.

Police said they arrested "over 20 people", bringing the total number of arrests to more than 200 since the protest movement exploded on 9 June.