Hong Kong police fired volleys of tear gas to disperse pro-democracy protests on Sunday and baton-charged a crowd blocking a key road in the government district in defiance of official warnings against illegal demonstrations.

Chaos had engulfed the city's Admiralty district as chanting protesters converged on police barricades surrounding more demonstrators who had earlier launched a "new era" of civil disobedience to pressureBeijing into granting full democracy.

Police, in lines five deep in places and wearing helmets and gas masks, used pepper spray against activists and shot tear gas into the air. The crowds fled several hundred yards, scattering their umbrellas and hurling abuse at police "cowards".

The demonstrators regrouped and returned however, and by early evening tens of thousands of protesters were thronging streets, including outside the prominent Pacific Place shopping mall that leads towards the Central financial district.

"If today I don't stand out, I will hate myself in future," said taxi driver Edward Yeung, 55, as he swore at police on the frontline. "Even if I get a criminal record it will be a glorious one."

Hong Kong returned to Chinese rule in 1997 under a formula known as "one country, two systems" that guaranteed a high degree of autonomy and freedoms not enjoyed in mainland China. Universal suffrage was set as an eventual goal.

But Beijing last month rejected demands for people to freely choose the city's next leader, prompting threats from activists to shut down Central in what is being seen as the most tenacious civil disobedience action since Britain handed over its former colony.

China wants to limit elections to a handful of candidates loyal to Beijing.

LEADER PLEDGES "RESOLUTE" ACTION

Police in full riot equipment later fired repeated rounds of tear gas to clear some of the roads in Admiralty and pushed the crowds towards Central. Health authorities later said some 30 people needed treatment.

Police had not used tear gas in Hong Kong since breaking up protests by South Korean farmers against the World Trade Organization in 2005.

"We will fight until the end...we will never give up," said Peter Poon, a protester in his 20s, adding that they may have to make a temporary retreat through the night.

Hong Kong leader Leung Chun-ying had earlier pledged "resolute" action against the protest movement, known as Occupy Central with Love and Peace.

"The police are determined to handle the situation appropriately in accordance with the law," Leung said, less than two hours before the police charge began.

A spokesperson for China's Hong Kong and Macau Affairs Office added that the central government fully supported Hong Kong's handling of the situation "in accordance with the law".

Communist Party leaders in Beijing are concerned about calls for democracy spreading to cities on the mainland, threatening their grip on power. Such dissent would never be tolerated on the mainland, where student protests in and around Beijing's Tiananmen Square calling for democracy were crushed with heavy loss of life on June 4, 1989.

On the mainland, the phrase "Occupy Central" was blocked on Sunday afternoon on Weibo, China's version of twitter. It had been allowed earlier in the day.

Later, a Hong Kong government statement urged the Occupy organizers to bring an end to the "chaos" for the overall interest of Hong Kong.

A tearful Occupy organizer Benny Tai said he was proud of people's determination to fight for "genuine" universal suffrage, but that the situation was getting out of control, RTHK reported. He said he believed he would face heavy punishment for initiating the movement.

Inside the cordon, thousands had huddled in plastic capes, masks and goggles as they braced for a fresh police attempt to clear the area before Hong Kong re-opens for business in the morning. The city's financial markets are expected to open as usual on Monday.

"WE WILL WIN WITH LOVE AND PEACE"

Publishing tycoon Jimmy Lai, a key backer of the democracy movement, said he wanted as big a crowd of protesters as possible, after a week of student demonstrations, to thwart any crackdown.

"The more Hong Kong citizens come, the more unlikely the police can clear up the place," said Lai, also wearing a plastic cape and workmen's protective glasses. "Even if we get beaten up, we cannot fight back. We will win this war with love and peace."

Pro-democracy Hong Kong lawmaker Lee Cheuk-yan said three fellow legislators were among a small group of activists detained by police, including democratic leaders Albert Ho and Emily Lau.

Organizers said as many as 80,000 people thronged the streets in Admiralty, galvanized by the arrests of student activists on Friday. No independent estimate of the crowd numbers was available.

A week of protests escalated into violence when student-led demonstrators broke through a cordon late on Friday and scaled a fence to invade the city's main government compound after a week of peaceful action. Police used pepper spray to disperse the crowd. The Hong Kong Federation of Students extended class boycotts indefinitely.

Police have so far arrested 78 people, including Joshua Wong, the 17-year-old leader of student groupScholarism, who was dragged away after he called on the protesters to charge the government premises.

Wong was released from police detention without charge on Sunday evening, the South China Morning Post reported. He told reporters that he planned to return to the protest site after resting.

His parents said in a statement the decision to detain him was an act of "political persecution".

Along with Hong Kong and Chinese officials, some of Hong Kong's most powerful tycoons have spoken out against the Occupy movement, warning it could threaten the city's business and economic stability.