During the Monday commemorations of the anniversary of the UK's handover of Hong Kong to China, a splinter group of protesters broke away from a peaceful demonstration and stormed into the LegCo building, vandalizing the interior.
They rammed the glass facade of the building before storming into the main parliamentary chamber and destroying property.
In a statement, a Hong Kong and Macau Affairs Office of the State Council spokesperson described the incident as "extremely violent", while Beijing expressed strong support to the Hong Kong government and local police in handling the incident in accordance with the law and investigating criminal responsibility of the offenders.
The Office added that Monday's incident infringes on Hong Kong's rule of law and called it a blatant challenge to the "one country, two systems" principle.
Embattled government officials emerged early on Tuesday, condemning the takeover of the city's legislature. Chief Executive Carrie Lam said she was "outraged and distressed" by the violence and anarchy, the South China Morning Post reported.
After visiting the LegCo headquarters on Tuesday, its President Andrew Leung told reporters that Parliament would be closed for at least two weeks as the electrical and fire safety systems of the building were damaged and repairs would take time, Efe news reported.
Leung said he and many others in Hong Kong were "sad" about the "violent actions" by protesters and said the LegCo premises resembled a big "crime scene".
Chinese Foreign Ministry spokesman Geng Shuang said the storming of the Legco building was "an unlawful act that trampled on the city's rule of law". Beijing urged the city to investigate what it called the "criminal responsibility of violent offenders".
Geng, asked to respond to US and EU comments on the storming, said it was "extremely hypocritical" for them not to oppose or reprimand violence in Hong Kong.
At a 4 a.m. press conference on Tuesday, Lam called the incident an "extreme use of violence and vandalism" and vowed to go after those who trashed the building and fled before the riot police moved in. Hundreds of policemen had to use tear gas to clear the building.
She compared the protesters' violence to a peaceful public march, also held on the day which marked the anniversary of Hong Kong's handover to China by the UK.
"We have seen two entirely different public scenes. One is a regular march on July 1... it was peaceful and generally orderly. This fully reflects the inclusiveness of Hong Kong society and the core values we attach to peace and order," Lam said at police headquarters.
"The second scene... is the extreme use of violence and vandalism by protesters who stormed into the Legislative Council building. This is something that we should seriously condemn."
Monday's disorder followed weeks of protests over a controversial extradition bill, which critics have said could be used to send political dissidents from Hong Kong to mainland China. The protesters are demanding the withdrawal of the bill, Lam's resignation and the release of all those detained in clashes with the police in protests.
According to the organizers of Monday's protests, around 550,000 people took part.
Although Monday's demonstration was not supposed to go near the area where the Parliament is situated, eventually a splinter group of protesters headed towards the LegCo and started battering the glass and metal security gates.
After four hours, the protesters - many wearing black clothes, gas masks and at points protected by people shielding their identities with umbrellas - managed to storm the building, including the main parliamentary chamber, where they defaced property then fled before riot police moved in.
On Tuesday morning, cleaning teams were seen clearing debris scattered around Parliament and nearby Tamar Park.
The LegCo building's outside walls were seen covered in graffiti, mainly targeting the divisive extradition bill, the government of Lam and alleged Beijing interference.
( With inputs from IANS )