The city has been plunged into its worst crisis in recent history by weeks of marches and sporadic violent confrontations between police and pockets of hardcore protesters.
Barricades going up around the #China central government liaison office in #HongKong as pro-democracy protestors escalate their actions and prepare for tonight’s inevitable clashes with riot police. pic.twitter.com/evRwsL5YmYStephen McDonell (@StephenMcDonell) July 21, 2019
The initial protests were sparked by a now-suspended bill that would have allowed extradition to mainland China.
The movement has since evolved, with protestors calling for democratic reforms, universal suffrage and a halt to the erosion of freedoms in the semi-autonomous territory.
Police have fired tear gas and rubber bullets, while the parliament has been invaded by protesters as Beijing's authority faces its most serious challenge since Hong Kong was handed back to China in 1997.
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Generally the marches have passed off peacefully, but some have been followed by violence between riot police and small groups of more hardcore protesters who feel years of peaceful demonstrations have achieved little.
Security was tightened in the city centre, with metal street fencing often used by protesters to build barricades removed ahead of the march, and large water-filled barriers thrown up around the police headquarters.
As Sunday's march came to an end, protesters occupied a major road next to the city's parliament and a large crowd gathered outside the police headquarters, which has previously been blockaded twice before.
A small contingent of riot police was on duty, and the atmosphere was described as calm.
The latest protests came a day after tens of thousands of people rallied in support of Hong Kong's police and pro-Beijing leadership in a stark illustration of the polarisation coursing through the city.
Under the 1997 handover deal with Britain, China promised to allow Hong Kong to keep key liberties such as its independent judiciary and freedom of speech.
But many say those provisions are already being curtailed, citing the disappearance into mainland custody of dissident booksellers, the disqualification of prominent politicians and the jailing of pro-democracy protest leaders.