Hong Kong (AFP) - Anti-government protesters in Hong Kong kicked off a new mass rally on Saturday as they defy increasingly stern warnings from China over weeks-long unrest that has plunged the city into crisis.

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 rallies and marches throughout the weekend and into next week, sending tensions soaring once more.

Thousands of protesters filled a park in the densely populated neighbourhood of Mongkok, which has previously seen clashes between police and demonstrators, listening to speeches and shouting slogans.

Police initially denied activists permission to march through the neighbourhood but later allowed it after an appeal.

Two marches are also planned for Sunday -- one on Hong Kong island and the other in the Tseung Kwan O district -- as well as a city-wide strike on Monday and rallies in seven locations.

The call for strike action appears to be gaining more traction than previous walkouts, with a host of organisations and unions vowing to join.

- Sliding freedoms -

Hong Kong has witnessed eight consecutive weekends of huge rallies -- often followed by violent clashes between police and small groups of hardcore protesters.

Under the terms of the 1997 handover deal, the city has rights and liberties unseen on the 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.

Story continues

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.

The past two weekends have seen a surge in violence used by both protesters and police, who have repeatedly fired rubber bullets and tear gas to disperse projectile-throwing crowds.

A mob of pro-government thugs also attacked protesters, putting 45 people in hospital.

Hong Kong's police have increasingly adopted tougher tactics, including this week charging 44 protesters with rioting -- an offence that carries up to 10 years in jail.

Hong Kong chief executive Carrie Lam has made few concessions beyond agreeing to suspend the extradition bill and has made few public appearances.

Protesters are demanding her resignation, an independent inquiry into police tactics, an amnesty for those arrested, a permanent withdrawal of the bill and the right to elect their leaders.

On Friday evening, thousands attended a rally organised by members of Hong Kong's usually tight-lipped civil service -- a remarkable development as they called on their paymasters to meet the protesters' demands.

Many civil servants wore surgical masks to hide their identities after the government warned that employees should show "total loyalty" and could be punished for attending.

Thousands of pro-government supporters also held a rally in a separate park on Saturday, many waving Chinese flags.