Police initially retreated as the protesters entered, avoiding a confrontation and giving them the run of the building, during which they spray painted slogans calling for a democratic election of Hong Kong's leader and denouncing the extradition legislation.
They ransacked the building, daubing its walls with anti-government graffiti, in an unparalleled challenge to city authorities and Beijing.
The smell of tear gas from the police's midnight eviction of the protesters had barely dispersed before the full-throated condemnation began.
Two of the demonstrators ferrying supplies in, 34-year-old marketer Amon and Lam Lam, a 20-year-old teacher, said they had heard rumours that the police would attempt to retake the complex but they were certain that there were none still in the building.
But the atmosphere deteriorated as the day wore on, and a hardcore group of protesters breached parliament after hours of siege.
In Hong Kong, the semiautonomous Chinese territory, protesters stormed and occupied the legislative building, selectively defacing any signs of Beijing's sovereignty after weeks of massive demonstrations.
Protesters also took down China's flag and replaced it with a black version of Hong Kong's flag, which features the white Bauhinia flower in the center.
Regina Ip, chairwoman of Hong Kong's pro-China New People's Party, said the protests had brought shame on Hong Kong.
The staggering difference represents a growing problem for Beijing: how long can and should Hong Kong be allowed to remain so defiant before it becomes ungovernable by Beijing's strict standards?
"We have to show the government that we won't just sit here and do nothing". The protesters know it.
A protest march has been called for later Monday, the third in three weeks.
But the increasingly hardline tactics from some protesters have alienated some, with a large counter-rally in support of the police taking place on Sunday.
China has denied interfering in Hong Kong affairs, though protesters have said the extradition bill is part of a relentless move towards mainland control. We've witnessed how Hong Kong has fallen in the past 22 years, how the city has continued to be mainlandized. However, the hundreds of masked protesters, mostly young people, blocked major roads while trying to interrupt an official flag-raising ceremony that is used to mark the anniversary every year.
If the principle is to defend the autonomy of Hong Kong and persuade Beijing to treat the special administrative region as a special case, British ministers can not be too heavy handed in how they project their interpretation of the Basic Law, Hong Kong's constitution. Hundreds of thousands took to the streets shouting for the complete withdrawal of the bill and the resignation of Chief Executive Carrie Lam.
Ms Lam showed little emotion as she stressed the importance of maintaining the rule of law in Hong Kong.
Monday's demonstrators left no doubt as to the future they prefer: They draped the city's pre-handover flag, featuring the UK Union Jack in its upper-left-hand corner, on the podium where the Legislative Council president sits.
Lam suspended the extradition bill on June 15 in a dramatic climbdown, saying she had heard the people "loud and clear", but stopped short of meeting the protesters' demands to scrap it and for her to step down. Kurt Tong made the comments Tuesday at an Independence Day celebration, where he also said "freedom of expression" is most effective and proper when exercised peacefully.
Jeremy Hunt - who is battling to become Britain's next Prime Minister - said today: 'We stand foursquare behind that agreement [the 1984 UK-Chinese declaration], foursquare behind the people of Hong Kong, and there will be serious consequences if that worldwide binding legal agreement were not to be honoured'.
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