Protesters tore down protective fencing around Hong Kong's Legislative Council building, smashed through glass doors and stormed offices Monday as demonstrations marking the anniversary of the former British colony's return to Chinese rule grew unruly.

Video from inside the legislative chamber showed protesters in hard hats milling about the chamber, spray-painting graffiti on the walls and tearing down pictures of leading lawmakers.

Police in riot gear fired tear gas to chase crowds away from the building but did not challenge those who breached the chamber. A first-ever "red alert" was issued for the legislature, warning everyone to evacuate the area, Hong Kong's South China Morning Post reported. The protesters occupying the chamber left after being warned they would be removed.

The unrest was the latest in a series of often huge and sometimes violent demonstrations against Hong Kong's leadership, centered around a proposal to change extradition laws to allow suspects to be sent to mainland China to face trial.

Mainland China's major state-run news outlets continued their trend of giving little coverage to weeks of protests in Hong Kong as residents of the semiautonomous city struggle to loosen the grip of the Beijing's government.

The chaos Monday briefly delayed a peaceful, pro-democracy march that drew hundreds of thousands to the city's center. Students and young people have led the protests, but support is broadly based. Retiree Lau Yeung-ching, 80, told the Morning Post he had to march "while I still can."

“I don’t agree with protesters using violence," he said. "But the vast majority of protesters are peaceful, and there is no justifying anti-riot police using excessive force such as rubber bullets on them.”

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Social worker Jackie Chen and Lun Chi-wai told the Hong Kong Free Press that many young people attacked the legislative building out of desperation.

“They have tried many kinds of protests … but there were no results," Chen said. "They really want to achieve something, but there are no methods."

The Hospital Authority said more than 50 people were treated for injuries.

Legislative Council President Andrew Leung Kwan-yuen, through a spokesman, chastised protesters for using “extremely violent means” to storm the complex and damage parts of the building. More than 40 lawmakers issued a statement condemning demonstrators' behavior.

“These extremely radical, violent elements seriously undermined social order and peace. They did these deliberately, disrupted public order and challenged the rule of law,” the statement said.

Earlier Monday, Hong Kong Chief Executive Carrie Lam joined brief ceremonies marking the 22nd anniversary of Britain relinquishing control of the densely populated city of more than 7 million people. She apologized again for her government's mishandling of the extradition bill, which she suspended June 15 after a wave of protests.

“This has made me fully realize that I, as a politician, have to remind myself all the time of the need to grasp public sentiments accurately,” she said in a five-minute speech to the gathering in the city’s cavernous convention center. "I will learn the lesson."

She insisted her government has good intentions but said, “I will learn the lesson and ensure that the government’s future work will be closer and more responsive to the aspirations, sentiments and opinions of the community.”

Foes want the law killed and Lam to step down. Democratic lawmaker Helena Wong Pik-wan repeatedly interrupted Lam, chanting, “Carrie Lam, step down, withdraw the evil law."

Hong Kong operates under a “one country, two systems” framework that was supposed to include the right to retain its own social, legal and political systems for 50 years after its handover to Chinese rule in 1997. The mainland government has steadily encroached on that autonomy.

Protesters demand an independent inquiry into police actions during a protest June 12, when officers used tear gas and rubber bullets to disperse protesters who blocked the legislature on the day debate on the extradition bill was scheduled to resume.

The police said the use of force was justified, but since then, they have largely adopted softer tactics, even as protesters besieged police headquarters, pelting it with eggs and spray-painting slogans on its outer walls.

Contributing: The Associated Press