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 protest march.
The ugly scenes in the financial hub also saw subway passengers 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 tried to continue onward.
Protesters threw eggs at the building and spray-painted its surrounding surveillance cameras, while 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 the protesters, many of whom scattered and went back in the direction of a key business district after clashes with police.
Police officers remained at the site and the force said on their official social media accounts that protesters threw bricks and petrol bombs at them and attacked the Central police station.
Hong Kong media released footage showing masked assailants, dressed in white with black masks pulled over the heads, attacking commuters in a subway station.
Screams rang out when the men attacked the subway passengers, according to footage taken by commuters and Democratic Party lawmaker Lam Cheuk-ting.
Lam, who was injured in the attack, said he was angry about a slow police response after he alerted them to the trouble, government-funded broadcaster RTHK reported.
Lam said the police action had failed to protect the public. "Is Hong Kong now allowing triads to do what they want, beating up people on the street with weapons?," he asked reporters.
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.
"This is absolutely unacceptable to Hong Kong as a society that observes the rule of law," the statement said, referring to the acts of the subway attackers as well as the protesters.
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.