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.