Hong Kong (AFP) - It started with an attempt Monday by hundreds of protesters to force a street vendor's trolley through the glass frontage of Hong Kong's parliament building.

In the locked interior of the lobby, dozens of police officers in full riot gear held the line for hours -- their colleagues occasionally dousing the protesters from above with pepper spray.

Time after time, the protesters attempted to ram the trolley through the entrance. It would give just a bit, the glass showing spider-web cracks.

The scene played out all day on television and social media -- on the 22nd anniversary of Hong Kong's handover to Beijing -- and TV also showed chief executive Carrie Lam earlier raising a glass of champagne as her colleagues sang the Chinese national anthem at a ceremony to mark the historic occasion.

Hours later, protesters had taken complete control of the Legislative Council -- the partially elected assembly dominated by pro-Beijing lawmakers.

The symbol of the defiance was a single anti-government protester spraying black aerosol over the Bauhinia flower that marks Hong Kong's flag and distinguishes the semi-autonomous territory from the mainland. 

The scene Monday was the culmination of nearly a month of massive anti-government protests sparked by opposition to a proposed law that would have allowed extraditions to China.

Those protests, however, have spiralled into sometimes violent agitation against authorities, and the action has been met by police using rubber bullets, batons and tear gas.

"We know that this is breaking the law, but we have no choice," a protester surnamed Cheung told AFP.

"We have to show the government that we won't just sit here and do nothing," added another, who gave her name as Joey.

Raucous scenes

Once protesters had breached the glass doors of "Legco", as the local assembly is known, police withdrew further behind lowered aluminium shutters.

But the protesters got through those soon after, and swiftly took over the historic chambers.

In raucous scenes, protesters wearing plastic helmets and face masks sat in the assembly seats normally occupied by nominated members representing constituencies including bankers, businessmen, developers, retailers and lawyers.

"There's no excuse for it," said Philip Dykes, of the Hong Kong Bar Association.

"Demonstrations must be peaceful, non-violent -- and if they're carried out in that theme and they are sufficiently massive the government will listen. I fear this is a step that's not necessary."

But protesters have shown little heed to authority in the current climate and Monday they tore up documents, scattering the pages like confetti around the chamber.

Four large black-and-white portraits of Lam and her closest cabinet colleagues and the city's police chief were pinned behind the speaker's podium under the slogan "There are no rioters, only tyranny".

Across the city, thousands of red flags bearing the "Bauhinia" flag had been raised in recent days, alongside the red and yellow-starred ensign of China.

Protesters, however, hijacked that theme Monday, and many carried black flags showing the Bauhinia's petals wilting.

In the assembly hall Monday, another group of protesters unfurled an old colonial Hong Kong flag.

The assembly's invasion lasted hours, with the police almost entirely absent.

But they were re-grouping after midnight, baton-charging protesters on a highway near the parliament building.