Hong Kong’s leader has warned that the city is on “the verge of a very dangerous situation” after protesters blocked roads and paralysed train services during morning rush-hour.
More than 14,000 people from 20 sectors vowed to join a city-wide strike on Monday, its organisers said.
Civil servants, who are ordered to be politically neutral, have reportedly agreed to take part.
At the airport, more than 200 flights were cancelled amid disruption fears.
The travel chaos follows the ninth consecutive weekend of protests in Hong Kong.
Violent clashes broke out between protesters and police, culminating in police firing tear gas.
In her first media address in two weeks, the city’s leader Carrie Lam said the protesters’ actions had challenged the principle of “one country, two systems” and were threatening prosperity and stability in Hong Kong.
She also accused activists of using a controversial extradition bill, which triggered the protests earlier in June, 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.”
Ms Lam reiterated that she would be not be stepping down – something protesters have repeatedly called for.
What have protesters planned for Monday?
On Monday morning, delays affected the Mass Transit Railway (MTR) as scuffles broke out between commuters and activists, who held open the doors to stop trains leaving. Several MTR lines have now been suspended.
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.
It is not yet clear how many have joined the planned city-wide strike, but several shops and businesses were closed on Monday – including international fashion retailers like Topshop and Zara.
As well as the strike, activists had scheduled rallies in seven different parts of Hong Kong on Monday.
Which flights are affected?
Most of the cancelled flights are with local carriers Cathay Pacific and Hong Kong Airlines.
Hong Kong airport, one of the busiest in the world, said travellers should check its website and seek updates directly from the airlines.
“The Airport Authority advises passengers to check with their airlines for the latest flight information, and 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 Ms Lam’s resignation, and the dropping of riot charges linked to the protests.
Hong Kong – a former British colony – is part of China but enjoys unique freedoms not available on the mainland.
Tensions rose further last week as more than 40 activists appeared in court charged with rioting, after protests that turned violent.
They could face up to 10 years behind bars if convicted.
China’s People’s Liberation Army (PLA) has so far stayed out of the protests, but China’s top policy office in Hong Kong has previously condemned the protests, calling then “horrendous incidents” that have caused “serious damage to the rule of law”.