Hong Kong student leader Joshua Wong has urged pro-democracy protesters to regroup in the heart of the city, less than a day after he announced he would go on hunger strike to demand electoral reform. Wong, 18, also urged the Hong Kong government to resume dialogue with students in the Chinese-controlled city a day after activists forced the temporary closure of government headquarters after clashing with police.

Protesters, who have occupied key streets for more than two months, have called on the city leader Leung Chun-ying to step down after Beijing in August ruled out a free choice of candidates for Hong Kong's next leader.

"This is not about withdrawing the National People's Congress decision made on August 31," Wong told reporters, referring to China's parliament. "We're asking the Hong Kong government to restart consultations on political reform."

Wong, who has been charged with obstructing court bailiffs during an operation to clear a protest camp in Mong Kok, across the harbour from Admiralty, is no stranger to protest movements.

Two years ago, with the help of secondary school activists calling themselves Scholarism, he forced the Hong Kong government to shelve plans to introduce a pro-China national education scheme in schools.

The pro-democracy protests, which started in late September and have lasted well beyond many people's expectations, drew more than 100,000 on to the streets of Hong Kong at their peak.

Chaos erupted on Sunday evening and spread into Monday as hundreds of protesters attempted to surround the central government offices and a road next door, during which police charged protesters with batons and pepper spray. Police said at least 40 arrests were made.

Hundreds of tents remain on the streets of Admiralty, next to government headquarters, where students have erected a makeshift village with study areas, supply stations and art displays.

Leung said on Monday police had been tolerant but would take "resolute action", suggesting that patience may be running out.

The democracy movement represents one of the biggest threats for China's Communist Party leadership since Beijing's 1989 crackdown on pro-democracy student protests in and around Tiananmen Square.

China rules Hong Kong under a "one country, two systems" formula that accords the former British colony a degree of autonomy and freedoms not enjoyed in mainland China, with universal suffrage set as an eventual goal.

The protesters are demanding free elections for the city's next leader in 2017 rather than the vote between screened candidates that Beijing has said it will allow.