Hong Kong riot police have dispersed pro-democracy demonstrators after they stormed into the main government complex in protest of the Chinese government tightening its grip on the former British colony.

Early on Saturday, police used pepper spray on protesters who forced their way through a gate and scaled high fences surrounding the compound to oppose Beijing's decision to rule out free elections for the city's leader in 2017.

At least 29 people were injured in the overnight protests, police said.

Protesters linked arms as police surrounded them with metal barricades with some chanting "civil disobedience" and "free the people".

At least four people were carried off on stretchers with slight injuries. The scene marked the biggest escalation in street protests since Beijing's decision in late August.

"We're still demanding universal suffrage," said Hong Kong Federation of Students leader Alex Chow.

Al Jazeera's Rob McBride, reporting from the complex, said that some protesters were still inside the compound on Saturday morning, while thousands remain outside.

Our correspondent said that the tense standoff continued and described the situation as "very fluid" with protesters reacting to the police moving their barricades forward.

Tensions escalate

The protest came after more than 1,000 school pupils rallied to support university students demanding full democracy for Hong Kong, capping a week-long campaign that has seen classroom strikes.

Earlier on Friday, hundreds of school children, some barely in their teens and dressed in school uniforms, assembled in a park close to government headquarters sporting yellow ribbons and stickers saying "smash Chinese Communist Party dictatorship".

About 200 students also camped outside the home of chief executive Leung Chun-ying on Thursday night after he ignored their 48-hour ultimatum to meet them to discuss the special administrative region's democratic future as tensions escalate.

After work on Friday evening, thousands more people rallied to the side of the 1,500 or so secondary pupils who had skipped classes, bringing the week-long class boycott to a close.

Source: Al Jazeera and agencies