Hong Kong media say more than 100 flights have been cancelled at the city's airport as a general strike called to support pro-democracy protests gets underway.
Public broadcaster RTHK said Monday that domestic carriers such as Cathay Pacific and Hong Kong Airlines were the most affected.
A citywide strike and demonstrations in seven districts in Hong Kong have been called for Monday afternoon. They follow a weekend of clashes with police on the streets.
Protesters stalled the morning rush hour by blocking train and platform doors to prevent trains from leaving stations.
Subway and train operator MTR said on Monday that service had been partially suspended on four lines because of the chaos.
It's the third time in three weeks that protesters have disrupted the train service.
Hong Kong has seen protests for two months. A movement against an extradition bill that would have allowed residents to be sent to mainland China to stand trial has expanded into demands for an investigation into alleged police abuse at protests and the dissolution of the legislature.
Hong Kong on verge of extreme danger: Lam
Hong Kong's embattled leader has warned that protests gripping the city are a challenge to China's sovereignty as strikes crippled transport and led to the cancellation of more than 200 flights.
Beijing-backed Lam addressed the media for the first time in two weeks after yet another weekend of violent protests and reiterated that the demonstrations were pushing the city to the verge of an "extremely dangerous situation".
Lam again rejected calls from protesters for her to resign and said the government would be resolute in maintaining law and order. She warned the protests were putting Hong Kong on a path of no return and had hurt the city's economy.
At the heart of the protest is a call for greater democracy.
Commuters struggled to get to work in the Monday morning rush hour before Lam spoke, with many rail and bus services suspended, while some activists blocked trains from leaving stations in the latest anti-government campaign.
Long lines of traffic could be seen across Hong Kong island leading into the heart of the business centre and hundreds of people were stranded at the airport.
Police arrested 44 people after sometimes violent clashes overnight when police fired tear gas to disperse demonstrators who moved swiftly across the city in flash mob-style actions.
The protests have at times shut government offices, blocked roads and disrupted business, posing the greatest political challenge to the former British colony since it returned to Chinese rule in 1997.
China's official Xinhua news agency said on Sunday: "The central government will not sit idly by and let this situation continue. We firmly believe that Hong Kong will be able to overcome the difficulties and challenges ahead".
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