Ugly scenes of violence have erupted outside Hong Kong’s parliament as protestors clashed with riot police after a massive demonstration against plans to allow extraditions to China.

An angry mob protesting plans to allow criminal suspects to be sent to China to face trial was met with pepper spray and police batons as they tried to storm the city’s parliament after hours of peaceful protest.

Police armed with riot shields moved in on them as they surrounded Hong Kong’s government headquarters after their permission to protest expired at midnight. They were warned earlier to leave the legislative area.

Officers and vans barricaded key entrances and called in reinforcements to prevent them from coming back.

Protesters reportedly struck back by using metal barricades against officers and by throwing bottles.

At least one police officer reportedly had blood streaming down his face.

In a late Facebook post, police said the protesters had deliberately caused damage to properties within the vicinity.

They added that it was illegal for the protesters to gather once the deadline for the public rally had expired.

Riot police shout at protesters during clashes after a rally against a controversial extradition law proposal in Hong Kong. Photo: Getty

More than 2000 officers mobilised for the mass demonstration which saw more than a million people march through the cramped streets of Hong Kong on Sunday in a noisy, colourful protest against the controversial extradition bill.

The turnout figure made it the city’s biggest rally since a similar number turned out in 2003 to challenge government plans for tighter national security laws, which were later shelved.

Protestors have vowed to continue fighting against the extradition law amendments which have been widely criticised as eroding the semi-autonomous Chinese territory’s judicial independence.

In the early hours of Friday, officers inside a patrolling police vehicle spotted a man holding an ignited glass bottle that he then threw toward the car before fleeing.

That afternoon, a man threw an ignited glass bottle toward the wall of a police station. It landed on the ground and erupted into flames.

Four men aged between 22 and 60 were taken into custody and the Hong Kong government said more people would be arrested.

Debates are expected to start on Wednesday over the amendments to the Fugitive Offenders Ordinance. The bill could be passed into law by the end of June.

Chants of “no China extradition, no evil law” echoed through the high-rise city streets, while other marchers called for Hong Kong’s Chief Executive Carrie Lam to step down.

Lam has tweaked the proposals but has refused to withdraw the bill, saying it is vital to plug a long-standing “loophole”.

Protesters are fighting to stop an amendment to extradition law. Photo: Getty

Insurance agents, executives and small entrepreneurs joined bus drivers and mechanics, with Reuters speaking to dozens of people saying it was their first protest march.

School teacher Garry Chiu joined the protest with his wife and one-year-old daughter, saying “it is no longer about me”.

“I need to save my daughter. If the law is implemented anyone can disappear from Hong Kong. No one will get justice in China. We know there is no human rights,” he said.

Sunday protests were also being planned in 25 cities globally, including London, Sydney, New York and Chicago.

The changes will simplify case-by-case arrangements to allow extradition of wanted suspects to jurisdictions, including mainland China, Macau and Taiwan, beyond the 20 that Hong Kong already has extradition treaties with.

But it is the prospect of renditions to mainland China that has alarmed many in Hong Kong. The former British colony was handed back to Chinese rule in 1997 amid guarantees of autonomy and freedoms, including a separate legal system.

Organisers and police were expecting up to 500,000 protestors. Photo: Getty

“It’s a proposal, or a set of proposals, which strike a terrible blow … against the rule of law, against Hong Kong’s stability and security, against Hong Kong’s position as a great international trading hub,” the last British governor, Chris Patten, said on Thursday.

-with AAP