"If this bill is not completely scrapped, I will have no choice but to leave my home, Hong Kong."
Opponents of the extradition bill, which would allow people to be sent to mainland China for trial in courts controlled by the Communist Party, fear it is a threat to Hong Kong's much-cherished rule of law.
Hong Kong returned to China under a "one country, two systems" formula that allows freedoms not enjoyed in mainland China, including freedom to protest and an independent judiciary.
Beijing denies interfering but, for many Hong Kong residents, the extradition bill is the latest step in a relentless march towards mainland control.
China has been angered by criticism from Western capitals, including Washington and London, about the legislation. Beijing said on Monday that Britain had no responsibility for Hong Kong any more and was opposed to its "gesticulating" about the territory.
THOUSANDS RALLY
Tens of thousands marched in temperatures of around 33 degrees Celsius (91.4°F) from Victoria Park in an annual rally. Many clapped as protesters held up a poster of Lam inside a bamboo cage. Organisers said 550,000 turned out.
More than a million people have taken to the streets at times over the past three weeks to vent their anger.
A tired-looking Lam appeared in public for the first time in nearly two weeks, before the storming of the legislature, flanked by her husband and former Hong Kong leader Tung Chee-hwa.
"The incident that happened in recent months has led to controversies and disputes between the public and the government," she said. "This has made me fully realise that I, as a politician, have to remind myself all the time of the need to grasp public sentiment accurately."
PROTEST MOVEMENT REINVIGORATED
Beijing's grip over Hong Kong has intensified markedly since Xi took power and after pro-democracy street protests that gripped the city in 2014 but failed to wrestle concessions from China.
Tensions spiralled on June 12 when police fired rubber bullets and tear gas at protesters near the heart of the city, sending plumes of smoke billowing among some of the world's tallest skyscrapers.
The uproar has reignited a protest movement that had lost steam after the failed 2014 demonstrations that led to the arrests of hundreds.
Activists raised a black bauhinia flag to half mast outside the Legislative Council building before the rally and turned Hong Kong's official flag, featuring a white bauhinia flower on a red background, upside down.
The turmoil comes at a delicate time for Beijing, which is grappling with a trade dispute with the United States, a faltering economy and tensions in the South China Sea.
Beyond the public outcry, the extradition bill has spooked some Hong Kong tycoons into starting to move their personal wealth offshore, according to financial advisers familiar with the details.