Hong Kong police have fired pepper pellets and made 300 arrests as thousands of people took to the streets to voice anger over national security laws proposed by China, that has raised international alarm over freedoms in the city.
In the heart of the financial district, riot police fired pepper pellets to disperse a crowd, and elsewhere in the city police rounded up dozens of protesters, making them sit on sidewalks before searching their belongings.
A heavy police presence around the Legislative Council deterred protesters planning to disrupt the debate of a bill that would criminalise disrespect of the Chinese national anthem.
Angry over perceived threats to the semi-autonomous city's freedoms, people of all ages took to the streets in scenes reminiscent of the unrest that shook Hong Kong last year.
"Although you're afraid inside your heart, you need to speak out," said Chang, 29, a clerk and protester dressed in black with a helmet respirator and goggles in her backpack.
Many shops, banks and offices closed early.
The latest protests follow the Chinese government's proposal for national security legislation aimed at tackling secession, subversion and terrorism in Hong Kong, terms officials in both Hong Kong and Beijing have used increasingly in regard to the pro-democracy protests.
The planned laws could see Chinese intelligence agencies set up bases in Hong Kong.
The proposal, unveiled in Beijing last week, triggered the first big street unrest in Hong Kong in months on Sunday, with police firing tear gas and water cannon to disperse protesters.
The United States, Britain, the European Union and others have expressed concern about the legislation, widely seen as a possible turning point for China's freest city and one of the world's main financial hubs.
But Chinese authorities and the Beijing-backed government in Hong Kong say there is no threat to the city's high degree of autonomy and the new security law would be tightly focused.
"It's for the long-term stability of Hong Kong and China, it won't affect the freedom of assembly and speech and it won't affect the city's status as a financial centre," Hong Kong Chief Secretary Matthew Cheung told reporters.
US President Donald Trump said on Tuesday the US would this week announce a strong response to the planned legislation.
China responded by saying it would take necessary countermeasures to any foreign interference.
Protesters in a downtown shopping mall chanted "Liberate Hong Kong! Revolution of our times" and "Hong Kong independence, the only way out".
As the protests in the financial district died down, hundreds of people gathered in the working class Mong Kok district on the Kowloon peninsula, where protests flared repeatedly last year.
Marchers briefly blocked roads before being chased away by police
About 300 people were arrested, most for illegal assembly, in three districts, police said.
Protesters and pro-democracy politicians say Hong Kong's National Anthem Bill, which aims to govern the use and playing of the Chinese anthem, represents another sign of what they see as accelerating interference from Beijing.
The bill carries penalties of up to three years jail and or fines of up to HK$50,000 ($A9745) for insulting the anthem. It also orders that school students be taught to sing the "March of the Volunteers", and learn its history.