Police in Hong Kong have been fighting running battles with activists in a third consecutive day of protests, after a call for a general strike caused widespread disruption on Monday.
Protesters blocked roads and paralysed train services at peak times on a day of action across the city.
More than 200 flights were cancelled as the protests entered their ninth week.
Hong Kong's leader, Carrie Lam, has pledged to restore law and order, rejecting calls for her resignation.
Initially the demonstrations, which began on 9 June, focused on a controversial extradition law, which would have allowed the transfer of suspects to mainland China. However, the protests have now become a wider challenge to Beijing's authority.
Ms Lam warned that Hong Kong was "on the verge of a very dangerous situation".
In her first media address in two weeks, Ms Lam said the protesters' actions had challenged the principle of "one country, two systems" - the extra freedoms granted to Hong Kong when it was returned from British to Chinese rule in 1997.
She also accused activists of using the extradition bill as a cover for their real goals.
"We continue to allow these violent protesters to make use of the [extradition] bill to conceal their ulterior motives," she said. "Those ulterior motives are going to destroy Hong Kong."
The Chinese foreign ministry said no one should underestimate China's resolve to safeguard the stability of Hong Kong, Reuters news agency reports.
What happened on Monday?
Police fired tear gas at several locations as protesters rallied into the night, setting fires and besieging police stations. In the North Point district, which has a reputation for pro-Beijing sympathies, men wielding long poles clashed with demonstrators before falling back.
More than 80 people were arrested, in addition to the 420 detained since 9 June. In that time, police said they had used more than 1,000 tear gas canisters and 160 rubber bullets.
Protest leaders had called for a general strike. While many people made it to work, in some areas protesters blocked trains from leaving stations and scuffled with commuters. Several lines of the Mass Transit Railway (MTR) were suspended for a time, and the Cross-Harbour Tunnel was also blocked.
One video circulating on Twitter reportedly showed a car in the district of Yuen Long forcefully hitting a barricade set up by protesters, injuring one person.
#breaking: A video circulated online has showed a car rushing through the barricades set up by #antiELAB protesters in #YuenLong and hitting at least a man #HKstrike #Hongkongprotests pic.twitter.com/LH8NhVy8DW— Jeffie Lam (@jeffielam) August 5, 2019
It is not clear how many joined the strike, but tens of thousands of protesters were out on the streets. Several shops and businesses were closed, including international fashion retailers like Topshop and Zara.
Hong Kong airport, one of the busiest in the world, said travellers should check its website and seek updates directly from the airlines.
Most of the cancelled flights were with local carriers Cathay Pacific and Hong Kong Airlines.
"The Airport Authority advises passengers... to proceed to the airport only when their seats and flight time have been confirmed," the airport said in a statement.
What's behind the Hong Kong protests?
The protests were initially sparked by a controversial bill that would allow China to extradite suspects from Hong Kong to the mainland.
Critics said it would undermine the territory's judicial independence and could be used to target those who spoke out against the Chinese government.
Although the bill has now been suspended, demonstrators want it fully withdrawn.
Their demands have broadened to include an independent inquiry into alleged police brutality, Ms Lam's resignation, and the dropping of riot charges linked to the protests.
Last week, more than 40 activists appeared in court charged with rioting. If convicted, they could be jailed for up to 10 years.
The Chinese army has so far stayed out of the dispute, but China's top policy office in Hong Kong has previously condemned the protests, calling them "horrendous incidents" that have caused "serious damage to the rule of law".