Tens of thousands of demonstrators have surrounded Hong Kong’s legislature, forcing it to postpone a second round of debate on an extradition bill that would allow people to be sent to mainland China for trial.

The protesters, mostly young and dressed in black, erected barricades as they prepared to hunker down for an extended occupation in scenes reminiscent of pro-democracy Occupy protests that rocked the city in 2014.

Many rallied on Wednesday in and around Lung Wo Road, a main east-west artery near the offices of embattled Chief Executive Carrie Lam, as hundreds of riot police warned them to stop advancing.

“We won’t leave until they scrap the law,” said one young man wearing a black mask and gloves.

“Carrie Lam has underestimated us. We won’t let her get away with this.”

Ms Lam has vowed to press ahead with the legislation despite deep concerns in the Asian financial hub, including among business leaders, that it could undermine freedoms and investor confidence.

Opposition to the bill on Sunday triggered Hong Kong’s biggest demonstration since its handover from British to Chinese rule in 1997 under a deal guaranteeing it special autonomy.

The government said debate on the bill that was due to take place in the city’s 70-seat Legislative Council would be delayed until further notice.

The legislature is controlled by a pro-Beijing majority.

Many of the protesters defied police calls to retreat and passed provisions, including medical supplies, goggles, water and food among each other.

Some stockpiled bricks broken away from footpaths.

The demonstrators rallied just a stone’s throw from the heart of the financial centre where glittering skyscrapers house the offices of some of the world’s biggest companies.

HSBC and Standard Chartered, in addition to the Big Four accounting firms, agreed to flexible work arrangements.

The government advised staff to avoid driving to work because roads were blocked as protesters vented their anger and frustration.

Demonstrators from across a wide spectrum of Hong Kong society began joining overnight protests earlier on Wednesday as businesses across the city prepared to go on strike.

Ms Lam sought to soothe public concerns and said her administration was creating additional amendments to the bill, including safeguarding human rights.

Sunday’s protest, which organisers said brought more than a million people to the streets, in addition to a snowballing backlash against the extradition bill, could raise questions about her ability to govern.

The protests have plunged Hong Kong into political crisis, just as the 2014 demonstrations did, heaping pressure on Ms Lam’s administration and her official backers in Beijing.

Britain handed Hong Kong back to China 22 years ago under a “one-country, two-systems” formula with guarantees its autonomy and freedoms, including an independent justice system, would be protected.

However, many accuse China of extensive meddling since then.

-AAP