Dozens of young pro-democracy activists forced their way into Hong Kong government headquarters as a week-long class boycott over Beijing's refusal to allow genuine democratic reforms ended in chaos.
The student protesters entered a square in the government complex, with some forcing their way through a security gate and others scaling a tall fence. The protesters pushed and shoved with officers, who they said responded with pepper spray.
Several people, including one police officer, were taken away on stretchers by medical personnel. Two students were arrested and about 200 protesters inside the square were surrounded by police, organisers said.
Hundreds of other protesters, many of whom had spent the strike's final day outside government headquarters, remained camped on the street outside after police regained control.
Thousands of university and college students who had spent the week boycotting classes were joined today by a smaller group of high school pupils.
Two students, including Joshua Wong, head of the activist group Scholarism, were arrested by police after entering the square.
The scenes of disorder came at the end of the week-long strike by students demanding China's communist leaders organise democratic elections in 2017.
Tension over Hong Kong's political future has risen significantly since control of the former British colony passed to China in 1997.
China's communist leaders have promised "universal suffrage" for the semi-autonomous region but last month ruled out letting the public nominate candidates, instead insisting they be screened by a committee of Beijing loyalists in a system that activists have branded "fake democracy".
Hong Kong's young people have been among the most vocal supporters of full democracy, fuelled by anger over widening inequality that they say dims their future prospects.