Hong Kong riot police fired tear gas yesterday evening at pro-democracy protesters in a popular tourist district, as violence rocked the international finance hub once more despite increasingly stern warnings from China.

The semi-autonomous southern Chinese financial hub 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.

Authorities in Hong Kong and Beijing this week signalled a hardening stance, including with the arrests of dozens of protesters, and the Chinese military saying it was ready to quell the "intolerable" unrest if requested.

But protesters have remained unyielding, vowing to hold multiple occupations and rallies in the coming days.

Yesterday's violence -- the ninth consecutive weekend of clashes -- took place in Tsim Sha Tsui, a usually bustling harbourside district known for its luxury malls and hotels.

Officers with gas masks and shields charged at hundreds of protesters who had been besieging a nearby police station.

Masked demonstrators had smashed the windows of cars in the 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.

Police fired volleys of tear gas followed by baton charges and made multiple arrests.

Earlier, protesters seized roads, built barricades and even briefly blocked a cross-harbour tunnel.

Hong Kong has witnessed two months of huge rallies -- often followed by violent clashes between police and small groups of hardcore protesters. And there is no sign of the chaos abating.

Many of the chants and graffiti tags thrown up yesterday called for residents to join a planned city-wide strike tomorrow.

Under the terms of the 1997 handover deal with Britain, the city has rights and liberties unseen on the Chinese mainland, including an independent judiciary and freedom of speech.

But many say those rights are being curtailed, citing the disappearance into mainland custody of dissident booksellers, the disqualification of prominent politicians and the jailing of pro-democracy protest leaders.

Public anger has been compounded by rising inequality and the perception that the city's distinct language and culture are being threatened by ever-closer integration with the Chinese mainland.