About 60 people were left injured, three badly, during Monday's protests in central Hong Kong that saw police clear the territory's legislature building of vandals using tear gas, the local government said Tuesday.

Meanwhile, the Chinese government, through its liaison office in Hong Kong, voiced "shock, indignation and strong condemnation" of the protesters' violent storming of the Legislative Council, saying it trampled on the rule of law and seriously undermined social stability.

It supported the Hong Kong government in "investigating relevant violent acts" and working to safeguard the autonomous territory's prosperity and stability.

Monday marked the 22nd anniversary of the former British colony's handover to China and the day descended into chaos after several hundred protesters managed to break through reinforced glass windows and a metal gate to enter the Legislative Council building in the afternoon.

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The legislative chamber's walls were spray painted with slogans such as "No to China extradition," "Release the martyrs" and "Carrie Lam step down." Some portraits were damaged.

Most protesters, including those who had occupied the legislature building, left before midnight. Police dispersed the remaining crowd shortly after midnight firing numerous tear gas canisters and charging at them.

Besides the protesters who were injured, 15 police officers were taken to hospital for treatment after having liquid and powder thrown at them.

At a press conference in the early hours of Tuesday, Hong Kong Chief Executive Carrie Lam condemned the storming of the legislature building and vowed to "pursue responsibility against those who committed illegal acts and broke the law."

Lam said she felt "angered and disheartened" to witness the acts carried out by the people who stormed and vandalized the building.

Sustaining extensive damages, Legislative Council President Andrew Leung said the legislature will be closed for at least two weeks.

"Being a civilized city, Hong Kong will not tolerate violence against the rule of law," Leung told reporters after touring the building that has remained to be a crime scene for police evidence gathering. "No matter one's opinion, no one should resort to violence to make one's views known."

The adjacent government headquarters have also been shut down for a day.

Pro-establishment lawmakers have jointly condemned the storming of the legislature building, while criticizing those who sympathize with the perpetrators.

"The breaking in, the vandalism at LegCo were clearly watched by many. We are jointly giving our strongest condemnation and urging police to pursue responsibility to the end," pro-establishment camp leader Martin Liao said.

But the pro-democracy camp lawmakers disagreed.

"We do not endorse vandalism, we do not condone violence," lawmaker Claudia Mo said. "But we hope the world will understand the desperation faced by Hong Kong's young people."

Kwok Ka-ki of the Civic Party said Lam is "evil-minded" in trying to divert public's attention from the government's failure to listen to the people.

Asked about the protests in Hong Kong, U.S. President Donald Trump said at the White House that he has discussed with Chinese President Xi Jinping over the issue and that it was "sad" to see a protest like this.

"(Hong Kong people) are looking for democracy, and I think most people want democracy. Unfortunately some governments don't want democracy. But that's what it's all about. It's all about democracy. There's never been anything better," Trump told reporters at the White House on Monday.

A protest march that according to organizers drew some 550,000 people also took place Monday to demand the complete withdrawal of an extradition bill that could facilitate the transfer of fugitives to mainland China. Hong Kong's government has said work on the bill has been halted, and that even if passed it would be allowed to expire in July 2020.

Police said turnout for the march was about 190,000.