The demonstrators had a standoff with Hong Kong police early Monday morning, blocking roads and attacking police officers with unidentified liquid.
They then smashed the glass walls of the Legislative Council building with a trolley and threw toxic powder at the police.
Some of them broke into the complex in the evening and vandalized the equipment inside the building's chamber.
Hong Kong Chief Executive Carrie Lam says she's saddened and shocked by the protesters' violent acts, which seriously impact on the core values of the rule of law.
"We want to tell you a shocking and sad thing here today. Some protesters stormed the Legislative Council building with the extreme use of violence in Hong Kong, a city that advocates law, peace, rationality and inclusiveness. I notice all the people condemn these violent acts no matter whether they share the same views or have different views on some policies or political stances. In Hong Kong, the rule of law is our most important foundation. So I hope you can condemn it here today with the community."
Lam says police showed restraint in handling the violence, but will investigate all illegal acts committed by the protesters and hold those responsible to account for their actions.
She also praised a peaceful march that took place on the same day, when over 160-thousand people showed up to support the police.
The chief executive says the march reflects the core values of peace and order, and hopes that normalcy will return soon.
Hong Kong Secretary for Security John Lee says the protesters who stormed the building may face various punishments.
"Anyone who violates the Legislative Council Ordinance and breaks in the Legislative Council building violates the law and will be imprisoned for three months at most. Those who commit forcible entry under the Public Order Ordinance will be sentenced a maximum imprisonment of two years. Under the Crimes Ordinance, possession of offensive weapons and possession of instruments fit for unlawful purposes and harming others are serious crimes."
Thirteen police officers were taken to hospital after being attacked with an unidentified liquid during the standoff with the protesters.
Hong Kong Commissioner of Police Stephen Lo.
"The protesters' violent acts have gone far beyond the bottom line of peaceful expression of demands. Police feel an extreme pity for that and strongly condemn it. Hong Kong is a society ruled by law. No violent act can be accepted by society. I believe many Hong Kong people are very disappointed and distressed about these violent acts."
Police have cleared roadblocks and driven off protesters who had occupied the Legislative Council building, and traffic flow on the main roads nearby have resumed.
For CRI, I'm Xie Cheng.
1. break into 强行进入；闯入；
The dog scared off intruders who had tried to break into the house.
2. account for 对（行动、政策等）负有责任；
The President and the President alone must account for his government's reforms.
3. at most 至多；最多；
We need 100 tons of cement at most for this project.
4. drive off 击退；赶走；
Men drove off the dogs with stones.