Clashes involving Hong Kong's protest movement escalated violently late Sunday as police launched tear gas at protesters who didn't disband after a massive march and subway riders were attacked by masked assailants who appeared to target the pro-democracy demonstrators.

The firing of tear gas was the latest confrontation between police and protesters who have taken to the streets for almost two months to fight a proposed extradition bill and call for electoral reforms in the Chinese territory.

The march had been peaceful when it reached its police-designated end point in Hong Kong's Wan Chai district in the late afternoon, but thousands continued onward, at various points occupying key government and business districts. They then headed for the Liaison Office, which represents China's Communist Party-led central government within the city.

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Protesters threw eggs at the building and spray-painted its surrounding surveillance cameras. China's national emblem, which adorns the front of the Liaison Office, was splattered with black ink. The Liaison Office said in comments published on Chinese state media that the acts "openly challenged the authority of the central government and touched the bottom line of the 'one country, two systems' principle."

Later, police threw tear gas canisters at protesters to try to disperse them. Protesters scattered, some heading back in the direction of a key business and retail district. Police remained in place, protecting themselves with shields. Police said on their official social media accounts that protesters threw bricks and petrol bombs at them and attacked the Central police station.

Protesters react to teargas as they confront riot police officers in Hong Kong on Sunday, July 21, 2019. Protesters in Hong Kong pressed on Sunday past the designated end point for a march in which tens of thousands repeated demands for direct elections in the Chinese territory and an independent investigation into police tactics used in previous demonstrations. Vincent Yu / AP

Hong Kong media released video showing masked assailants attacking commuters in a subway station. Among those attacked were protesters clad in their trademark black clothing and yellow hard hats.

The attackers, meanwhile, were dressed in white with black masks pulled over their heads. On Saturday, demonstrators wore white at a counter-rally in support of police.

The Hong Kong government said in a statement shortly after midnight that commuters were attacked at a subway station in the city's Yuen Long neighborhood, leading to "confrontations and injuries."

The statement also said some "radical protesters initiated a series of violent acts ... despite repeated warnings" by police. They said the acts included hurling petrol bombs, setting fires and throwing bricks.

Organizers said 430,000 people participated in Sunday's march, while police said there were 138,000 during the procession's "peak period."

Large protests began early last month in opposition to a contentious extradition bill that would have allowed Hong Kong residents to stand trial in mainland China, where critics say their rights would be compromised.

Hong Kong's leader, Carrie Lam, has declared the extradition bill dead, but protesters are dissatisfied with her refusal to formally withdraw the legislation. Some are also calling for her to resign amid growing concerns about the steady erosion of civil rights in the city.

While the demonstrations have been largely peaceful, some confrontations between police and protesters have turned violent. In Sha Tin district the previous Sunday, they beat each other with umbrellas and bats inside a luxury shopping center. Demonstrators broke into the Legislative Council building on July 1 by moving past barricades and shattering windows.

On Friday, Hong Kong police discovered a stash of a powerful homemade explosive in a commercial building and arrested a man. Materials voicing opposition to the extradition bill were found at the site, local media said, but a police spokesman said no concrete link had been established and the investigation was continuing.

The People's Daily, the Communist Party's official newspaper, condemned "radical extremists" who attacked the legislature and "trampled" on Hong Kong's rule of law in a front-page column Sunday. The paper said the counter-rally Saturday intended to show support for the police reflected "mainstream public opinion" in Hong Kong.