Thousands of secondary school and university students have boycotted classes on the first day of the new school year.
Organisers estimate that 10,000 secondary students from 200 schools are taking part.
The student action comes on the same day as a call for a general two-day strike and large rally.
Protests over the weekend saw some of the worst violence in weeks between protesters and police.
On Saturday, protesters had thrown petrol bombs, lit fires and attacked the city’s parliament building while police used tear gas, rubber bullets, water cannons and fired live warning shots in an attempt to disperse crowds.
Hong Kong is now entering its 14th successive week of demonstrations. The protests were sparked by changes to a law that would allow extradition to mainland China, but have since widened to include calls for an independent inquiry into police brutality and universal suffrage.
Rallies across Hong Kong
Early on Monday, protesters disrupted train services at different stations causing major rush hour traffic delays. Services resumed later on Monday morning.
Later in the morning, secondary school students gathered at Edinburgh Place in the city’s central district.
“I am willing to take any disciplinary consequences,” one student from a college in the district of Sham Shui Po told Hong Kong newspaper South China Morning Post.
Images on social media also showed students forming human chains outside several secondary schools in the city.
At the Chinese University of Hong Kong (CUHK), hundreds of university students have also begun gathering to protest.
The university’s Student Union said in a Facebook statement that a “city-wide class boycott” would be held later on Monday at CUHK’s University Mall.
The union said the university had “contacted” them to cancel the rally but that they would “maintain our original plan”.
The student protests are part of a general two-day strike beginning on Monday with another large rally planned for the afternoon.
A weekend of violence
Monday’s strike comes as the city is still reeling from a weekend of protests that turned into violent clashes between police and activists.
On Sunday, pro-democracy protesters blocked roads to the city’s airport, disrupting the operation of the major Asian transport hub.
Trains to the airport were halted and roads blocked so that passengers had to walk to the terminal. Most flights operated as normal, but delays were reported.
On Saturday, police and protesters clashed during a banned rally.
Hong Kong riot police used tear gas, rubber bullets and water cannon to disperse crowds as tens of thousands marched in the city, defying a ban.
Officers also fired live warning shots as they tried to clear the streets.
Protesters lit fires, threw petrol bombs and attacked the parliament building. A number of people were later held as they fled into metro stations.
The weekend protests and Monday’s strike action comes after several key pro-democracy activists and lawmakers were arrested last Friday.