Clashes between protesters and police have broken out in Hong Kong, cutting short a rally after thousands gathered at a park to call for greater democratic freedoms in the Chinese-ruled city.

Riot police on Sunday fired tear gas at protesters and arrested several people near the park, known as Chater Garden after some demonstrators attacked plain-clothes officers.

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Authorities had allowed the rally as long as those taking part stayed in one location. Police warned they would stop anyone attempting to march.

Protesters spilled onto the streets, sporting their movement's trademark black clothing and face masks. Some barricaded the roads with umbrellas and street furniture, dug up bricks from the pavement and smashed traffic lights.

Two police officers were attacked with wooden sticks and sustained head injuries, forcing the police to sweep into the area and to fire tear gas to disperse the crowds.

Ventus Lau, the rally organiser, was arrested for allegedly violating the police's condition for the rally.

A woman cries as she pleads with the police not to beat a man as police detain protesters in Hong Kong [Ng Han Guan/AP]

'Free Hong Kong!'

Earlier, protesters packed into Chater Garden, located near the city's Legislative Council building, holding up signs that read: "Free Hong Kong".

They chanted "we want real universal suffrage" and "disband the police force". Some waved American, British and Hong Kong independence flags.

The frequency and ferocity of Hong Kong's protests have died down over the last month, but signs of political unrest are everywhere, from graffiti daubed on walls to huge fences surrounding government buildings.

In an apparent new tactic, police have been showing up ahead of time in riot gear, with officers conducting "stop and search" operations near expected demonstrations.

"Everyone understands that there's a risk of stop-and-search or mass arrests. I appreciate Hong Kong people still come out courageously, despite the risk," said Lau before being arrested.

Hong Kong's protests have raged for seven months after being sparked by a now-abandoned proposal to allow extraditions to the authoritarian mainland China, where the opaque legal system answers to the ruling Communist Party.

They soon morphed into a wider movement calling for greater freedoms in what is the most concerted challenge to Beijing's rule since the former British colony's 1997 handover.

Clashes broke out between protesters and police after demonstrators marched in defiance of a ban [Ng Han Guan/AP]

Critics accuse Hong Kong's police of using excessive force, with no police officer disciplined or punished in the last seven months of protests.

Police say they have used force commensurate with the levels of violence they face from hardcore protesters who routinely throw bricks and petrol bombs.

Among key demands of the protest movement is an independent inquiry into the police, an amnesty for 7,000 people arrested and fully free elections.

Beijing and local leader Carrie Lam have refused further concessions and defended police tactics.