The mainly young and masked protesters also barricaded key roads in Admiralty and Wan Chai and attacked police with what was suspected to be drain cleaner and caustic soda, and also launched eggs and bottles at them in other clashes.
The ugliest scenes were at Legco in Admiralty, where violence continued for half the day.
Before 9pm, protesters broke through the entrance and ransacked the legislature. Some were equipped with wooden sticks while others transported supplies such as helmets.
They earlier dismantled a metal fence at the building, breaking into the car park area of the compound, as others tried to smash the glass doors of the main public entrance using metal bars they got from dismantling barricades set up outside the complex.
Some threw bricks and metal rods at the doors, while others heckled police inside.
Shouts of “add oil” for encouragement echoed through the area as protesters battered the doors. At first, the security roller shutters of the main entrance were breached but the protesters initially did not enter.
Behind the shutters, police officers stood in full riot gear. Their warnings to the protesters were drowned out by the noise. About 1,000 riot police stationed in the legislature retreated when radicals broke into the Legco complex, the Post was told.
The attack on the main public entrance came about an hour after protesters tried to force their way into the Legco block by ramming a metal cart through a glass door at the members’ entrance on the other side of the compound. Police responded with pepper spray.
But the protesters’ bid was finally successful, leaving a gaping hole in the glass door. But they looked confused and just left.
Earlier in the day, one protester was reportedly pushed to the ground as he tried to stop others from attacking the building.
Opposition lawmaker Leung Yiu-chung was also seen trying to stop the protesters but to no avail. He was also knocked over.
Other pro-democracy lawmakers, including Roy Kwong Chun-yu and Lam Cheuk-ting, were also at the scene pleading for the protesters to remain peaceful. But their appeals fell on deaf ears.
In a statement issued shortly before 7pm, the government said it “strongly condemns and deeply regrets the extremely violent acts committed by some protesters who stormed the Legislative Council complex … using a roll cage trolley as a ram and iron poles to shatter glass doors of the Legco”.
A government spokesman said Hong Kong “is a society that respects the rule of law, and has never tolerated violence.
“The police will take appropriate enforcement action to protect public order and safety.”
Police also condemned the violence.
At about 6pm, Legco issued a red alert, telling everyone to evacuate the building.
The compound is just a stone’s throw from the government headquarters and the office of the city’s leader, Carrie Lam Cheng Yuet-ngor. The site has been at the centre of protests for weeks, driven by demands for the withdrawal of the now-suspended extradition bill and for Lam to step down.
It was by far the worst damage at the Legco building since November 2014 when radical protesters stormed the legislature, smashing two glass doors at the height of the Occupy protests.
On June 12, some anti-extradition bill protesters clashed with police outside the building, with officers using tear gas, rubber bullets and beanbag rounds. The compound was intact.
Monday’s violence contrasted with the many largely peaceful anti-bill rallies in previous weeks.
The protesters, apparently not affiliated with mainstream political groups, use social media to exchange information, organise and even for votes on their next moves.
In one Telegram group with more than 20,000 members, some expressed disapproval of storming the legislature.
“What’s the purpose of smashing the glass?” one asked in a post. Another message read: “What are they doing? They have wasted the students’ efforts!”
Some even suspected they were “spies” to give the government an excuse to suppress their movement.
But there were also people calling for unity. One post read: “If we manage to storm Legco, it means we have the ability to overthrow the government. Carrie Lam has been ignoring us because she thinks we are harmless. Now their [action] is meant to tell Carrie Lam: ‘If you don’t respond to our appeals, we will tear down your house.’”
Meanwhile, as protesters were trying to break into the legislature, a woman tried in vain to persuade her radical counterparts to stop. “What do you think you can do even if you make it inside Legco?” she shouted at the mob. “You don’t have the manpower to fight the police. They are armed with guns!”
Another protester, John Lo, 35, who went to the complex after joining the annual July 1 march, said: “I am here because I am a Hong Kong citizen and it is my civil responsibility. Carrie Lam must step down and be responsible for the troubles she has caused to Hong Kong.”
If we manage to storm Legco, it means we have the ability to overthrow the government
Lo said he regarded those storming Legco as his “comrades” but he wished they had not done so.
There had been other incidents earlier in the day. Police used pepper spray and batons against protesters who had occupied key roads ahead of a flag-raising ceremony in Golden Bauhinia Square in Wan Chai to mark the city’s handover anniversary.
The protesters used mills barriers and other items to block roads while some stole iron poles and bricks from a nearby construction site and took railings from streets. At about 7.30am, protesters charged police lines. Officers responded with pepper spray.
Some protesters hurled objects containing unknown liquid at officers. Officers at scene were injured and among them, some experienced difficulty in breathing and had swollen skin. Police sources said they suspected the liquid might be drain cleaner.
Thirteen officers had to be sent to hospital for treatment and were later discharged.
Reporting by Karen Zhang, Su Xinqi, Chris Lau, Phila Siu, Sum Lok-kei, Alvin Lum, and Ng Kang-chung