Hundreds of protesters have stormed Hong Kong's parliament, destroying pictures and daubing walls with graffiti on the anniversary of the city's 1997 return to Chinese rule.

Key points: The clash is seen as one of the most violent to rock the city in decades

The clash is seen as one of the most violent to rock the city in decades Protesters are demanding Hong Kong leader Carrie Lam's resignation

Protesters are demanding Hong Kong leader Carrie Lam's resignation It is unclear if any arrests have been made

Protesters whacked away at thick glass windows until they shattered and then pried open steel security gates.

The three-hour occupation of the Legislative Council ended after police began firing tear gas shortly after midnight.

About a thousand protesters, furious at a proposed law allowing extraditions to China, were gathered around the building in the former British colony's financial district in a direct challenge to authorities in Beijing.

Protesters try to break into the Legislative Council building where riot police are seen. ( Reuters: Tyrone Siu )

The day after the protest, a representative of China's Hong Kong affairs office labelled the actions of some protesters an "undisguised challenge" to the one country, two systems formula.

Pro-Beijing politicians in Hong Kong also condemned the damage done by the protesters.

Regina Ip, a former security secretary in the semi-autonomous territory, said such behaviour was not acceptable in "civilized society".

She said there was nothing that could justify "the sort of violence we saw".

Protesters held up umbrellas to protect themselves or fled, while plumes of smoke billowed across major thoroughfares and between skyscrapers.

Officers eventually entered the legislative chambers after protesters had already left. It was not clear if any arrests were made.

Most demonstrators had been cleared by the early hours of Tuesday morning after some of the most violent protests to rock the city in decades.

Protesters put up a Hong Kong colonial flag and defaced the Hong Kong logo at the Legislative Chamber. ( AP: Vincent Yu )

Umbrellas, metal barriers, hard hats, water bottles and other debris lay strewn across major roads.

Protesters had carried road signs, corrugated iron sheets and pieces of scaffolding as they barged into the council building.

Some sat at legislators' desks, checking their phones, while others scrawled "anti-extradition" on chamber walls.

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Other graffiti called for Hong Kong leader Carrie Lam to step down, while pictures of some politicians were defaced.

Banners hanging over flyovers at the protest site read: "Free Hong Kong."

Lam condemns 'violence' and 'vandalism'

Protesters defaced the Hong Kong emblem and posted political slogans inside the building. ( AP: Kin Cheung )

A small group of mostly students wearing hard hats and masks had used a metal trolley, poles and scaffolding to smash their way through the legislative compound's reinforced glass doors.

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The protesters, some with cling film wrapped around their arms to protect them from tear gas, also paralysed parts of the Asian financial hub as they occupied roads after blocking them off with metal barriers.

The Government called for an immediate end to the violence, saying it had stopped work on amendments to the suspended extradition bill and that the legislation would automatically lapse in July next year.

The Legislative Council Secretariat released a statement cancelling business for today, as did the central government offices, which said they would close "owing to security consideration".

Ms Lam called a 4:00am press conference the morning after the chaos, where she condemned the "violence" and "vandalism" of protesters who stormed the territory's legislature.

"This is something we should seriously condemn," she said.

Ms Lam also said police, who initially retreated as protesters entered the parliament building, had exercised restraint in dealing with the demonstrations.

Police officers took control of the meeting hall of the Legislative Council in the early hours of Tuesday. ( AP: Kin Cheung )

Ms Lam suspended the extradition bill on June 15 but stopped short of protesters' demands to scrap it.

It was not immediately clear if the announcement would eventually ease the tension.

The Beijing-backed leader is clinging to her job amid an unprecedented backlash against the Government.

Opponents of the extradition bill, which would allow people to be sent to mainland China for trial in courts controlled by the Communist Party, fear it is a threat to Hong Kong's much-cherished rule of law.

The wave of discontent poses the greatest popular challenge to Chinese leader Xi Jinping since he came to power in 2012.

Calls for restraint

Hong Kong returned to China under a "one country, two systems" formula that allows freedoms not enjoyed in mainland China, including freedom to protest and an independent judiciary.

Beijing denies interfering but, for many Hong Kong residents, the extradition bill is the latest step in a relentless march towards mainland control.

A portrait of a former legislative leader was damaged after protesters broke into the Legislative Council building. ( AP: Vincent Yu )

China has been angered by criticism from Western capitals, including Washington and London, about the legislation.

Beijing said on Monday that Britain had no responsibility for Hong Kong any more and was opposed to its "gesticulating" about the territory.

The European Union on Monday called for restraint and dialogue to find a way forward.

Rallies have seen more than a million people on the streets

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 1 minute 7 seconds 1 m 7 s Protesters began breaking into the government's headquarters earlier in the day.

Monday's protests began with tens of thousands of people marching in temperatures of around 33 degrees Celsius from Victoria Park in an annual rally.

Organisers said 550,000 turned out but police said there were 190,000 at their peak.

More than a million people have taken to the streets at times over the past three weeks to vent their anger.

Ms Lam contrasted the earlier demonstration with the storming of the legislature, saying the two protests had shown "two entirely different public scenes".

Pro-democracy politicians and the protest organiser said Ms Lam has ignored the demands of the people and pushed youngsters towards desperation, despite pledging to listen to people's demands.

Police inside Hong Kong's Legislative Council stand back after protesters smash through windows. ( AP: Vincent Yu )

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