Hundreds of protesters have clashed with police in Hong Kong, as demonstrators stepped up a street campaign pushing for free elections and democratic reforms in the Chinese-controlled city state.

Police officers armed with pepper spray, batons and riot shields charged at the protesters as they tried to disperse them, making at least 40 arrests in the scuffles. Demonstrators stormed past police lines overnight on Sunday as they tried to surround government headquarters, erecting new barricades from metal railings and plastic cable ties. As a result, the central government offices and the legislature were forced to temporarily close on Monday morning.

Al Jazeera's Sarah Clarke reporting from Hong Kong Right now (05:00 GMT), it is relatively peaceful compared to the violent scenes we saw last night. The police have retreated and some of the barricades have been removed. There have been some small outbursts in various areas where one particular protester was removed from the scene in a stretcher. But peace has been restored as we wait for the next move from either side. Police have issued a statement condemning the protests’ organisers who they say are inciting the violence against the officers. Protesters and organisers say the level of violence and tactics used by the police last night were unnecessary and unfortunate.

As morning approached, police began clearing roads leading to government offices, scattering protesters and demolishing their tents following the overnight clashes.

The latest flare-up between police and protesters marks an escalation in the civil disobedience movement that first started three months ago. It also underscores the frustration of protesters at Beijing's refusal to budge on electoral reforms and grant greater democracy to the former British colony.

The protesters are demanding free elections and to be allowed to choose their candidates for the 2017 elections without interference from Beijing while China's communist authorities insist candidates for the 2017 vote must be vetted by a loyalist committee.

Al Jazeera's Rob McBride, reporting from Hong Kong, said hundreds of police had cleared the area by Monday morning, pushing protesters back more than 200 metres.

Our correspondent said it was the worst outbreak of violence since protests began in late September, with police eager to clear the site before the Monday morning rush-hour.

Police had earlier warned they would not let the protesters "illegally occupy" Lung Wo Road, a major thoroughfare that connects the east and west of Hong Kong.

McBride reported that police lost control of the main protest site, as several hundred demonstrators spilled over into the streets.

Student protest leaders told thousands rallying at the main protest site outside the government headquarters that they would escalate their campaign.

Protesters said they would occupy the road until Monday morning to prevent Leung and other government officials from getting to work.

The protests drew tens of thousands of people at times during their first weeks, but the number of protesters have dwindled as the movement's leaders struggle to keep up momentum.

A riot police officer holds a baton as he attempts to clear a demonstration site close to the office of the chief executive [Reuters]