Police in Hong Kong clashed with throngs of protesters outside government buildings Wednesday as opposition intensified to a proposed extradition bill that would tighten Beijing’s control over the semiautonomous territory.

The legislation, if approved, would allow Hong to Kong to extradite suspected criminals to jurisdictions outside Hong Kong without a prior agreement – notably mainland China.

The violence came after government officials delayed the opening of debate on the bill, which has drawn the ire of students and others in the economically free-wheeling city of more than 7 million people.

The crowd overturned barriers and threw objects at police,who countered with rubber bullets and tear gas. 

Earlier, a government statement said the legislative session scheduled to begin at 11 a.m. Wednesday – 11 p.m. ET Tuesday – would be “changed to a later time.” Hong Kong leader Carrie Lam canceled a news briefing.

More: Hundreds of thousands are protest in in Hong Kong. Here’s why

The U.S. State Department this week expressed “grave concern” over the proposal, saying it could threaten Hong Kong’s “special status” with the mainland. That brought a sharp response from Beijing on Wednesday, with Foreign Ministry spokesman Geng Shuang saying no country has a right to interfere in its internal affairs.

“We ask the U.S. side to adopt a fair and objective attitude with regard to the lawful amendment of the ordinances by the Hong Kong SAR government, be discreet in its words and actions and stop interfering in Hong Kong affairs and China’s internal affairs in any form,” he said.

The legislation was triggered by a homicide case last year. Taiwanese authorities were unable to prosecute a Hong Kong man accused of killing his pregnant girlfriend in Taipei because he fled to Hong Kong. Taiwan’s Mainland Affairs Council, in support of Hong Kong’s special status, has decried the legislation, however, threatening to post a travel advisory for Hong Kong if the bill becomes law.

The protests are the largest since pro-democracy demonstrations closed down parts of the Asian financial center for more than three months in 2014. Some businesses closed for the day, and labor strikes and class boycotts were called.

The protests are a challenge to China’s ruling Communist Party and President Xi Jinping, who has in the past said he would not tolerate Hong Kong being used as a base to challenge the party’s authority.

Samuel So, who is involved in the protest efforts and is a former resident of Hong Kong, said its citizens’ very identities are threatened.

“This is such a unique identity that we are fighting for,” So said.

On Sunday, hundreds of thousands of demonstrators gathered against the bill in one of Hong Kong’s biggest protests in recent history. People of all different backgrounds marched together peacefully until a smaller group clashed with the police outside the government headquarters. 

The legislation has caused internal strife within the city, even prompting physical violence when lawmakers for and against the bill battled over access to the chamber. 

Chief Executive Lam, however, has claimed the amendments are necessary to close legal loopholes, while opponents worry it will allow China to undermine Hong Kong’s fragile political status and target dissidents. 

At a brief news conference held as the chaos swirled just outside, Police Commissioner Stephen Lo Wai-chung called the demonstration a riot. That could spell long jail terms for anyone arrested, adding to concerns that Hong Kong’s government is using public disturbance laws to intimidate political protesters.

“We condemn such irresponsible behavior,” Lo said. “There’s no need to hurt innocent people to express your opinions,” he said, adding that people should not “do anything they will regret for the rest of their lives.”

Police spokesman Gong Weng Chun defended the decision to use tear gas and other non-lethal weapons to quell the demonstration.

“I believe that if our officer is not encountering some threat that they probably may suffer from serious bodily harm or even our officer thinks that their life is being threatened, I don’t think our officer has any necessity to use any kind of force,” he said.

More: If Hong Kong extradition bill passes, what will happen?

A protester, who gave her name only as King, also out of fear of repercussions, said the protest was a watershed moment for Hong Kong’s young generation.

“We have to stand up for our rights or they will be taken away,” she said.

Dressed in black T-shirts and jeans, many protesters appeared undaunted by demands to disperse from police. The demonstrators also appeared mindful of Beijing’s growing use of electronic surveillance such as facial recognition technology to build dossiers on those it considers politically unreliable, with many donning surgical or anti-pollution masks to hide their features, as well as to safeguard against tear gas.

Such protests are never tolerated in mainland China, and Hong Kong residents can face travel bans and other repercussions if they cross the border.

More: US Secretary of State Mike Pompeo ‘smears’ China on 30th anniversary of Tiananmen Square protests

Under its “one country, two systems” framework, Hong Kong was supposed to be guaranteed the right to retain its own social, legal and political systems for 50 years following its handover from British rule in 1997. However, China’s ruling Communist Party has been seen as increasingly reneging on that agreement by forcing through unpopular legal changes.

Contributing: The Associated Press