Anti-government protesters in Hong Kong seized the parliament's main debating chamber late Monday, daubing its walls with graffiti and fixing a British colonial-era flag to the main podium, an AFP reporter on the scene said.
Dozens of masked protesters stormed into the chambers after successfully breaching the complex's reinforced glass windows, shouting slogans and spraying the city's coat of arms with black paint.
A black and white banner hoisted in the chamber read in Chinese: "Bow to protect rule of law. Oppose extradition."
The protesters started leaving after a couple of hours as police warned they would use force to evict them.
The police later used tear gas as they charged into the building and retook control.
The financial hub has been rocked by three weeks of huge demonstrations against an unpopular bill that would allow extraditions to the Chinese mainland.
- 'We have no choice' -
Many protesters said they felt compelled to take the action because the city's pro-Beijing leaders had ignored public sentiment following marches against the loathed extradition law.
"We have marched, staged sit-ins... but the government has remained unmoved," Joey, a 26-year-old protester, told AFP as he walked over shattered glass inside the building.
"We have to show the government that we won't just sit here and do nothing."
A protester surnamed Cheung, 24, added: "We know that this is breaking the law, but we have no choice".
The past three weeks of rallies are the sharpest expression of fears over Chinese influence on the territory in decades.
Protesters accuse Beijing of stamping down on the city's freedoms and culture with the help of the finance hub's unelected leaders.
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.
Although Hong Kong returned from British to Chinese rule on July 1, 1997, it is still administered separately under an arrangement known as "one country, two systems".
The city enjoys rights and liberties unseen on the autocratic mainland, but many residents fear Beijing is already reneging on that deal.
Activists have organised a march every handover anniversary, calling for greater democratic freedoms -- such as the right to elect the city's leader.
They have mustered large crowds in recent years -- including a two-month occupation of parts of the city centre in 2014 -- but have failed to win any concessions from Beijing.
This year's rally is framed by unprecedented anti-government protests that have drawn millions, with the public angry over police use of tear gas and rubber bullets.
The spark for the current wave of protests was an attempt by chief executive Carrie Lam to pass the Beijing-backed extradition law, which she has now postponed following the public backlash.
But she has resisted calls to permanently shelve the law or step down.
As a result the demonstrations have morphed into a wider movement against her administration and Beijing.
- Champagne toasts & flags -
Lam -- who has kept out of the public eye since her climbdown and has record low approval ratings -- attended a flag-raising ceremony early Monday, marking the moment the city returned to Chinese ownership 22 years ago.
Her speech stuck to the conciliatory tone she has used in recent weeks saying she recognised conflict had broken out.
"It has made me fully understand that as a politician, I need to be aware and accurately grasp the feelings of the people."
Britain's Foreign Secretary Jeremy Hunt said his country's support for Hong Kong and "its freedoms is unwavering" and urged restraint from protesters in comments echoed by the European Union.
But activists have vowed to keep up their civil disobedience campaign.
"Whatever happens we won't lose heart," Jason Chan, a 22-year-old accountant added. "Resistance is not a matter of a day or a week, it is long term."