* Tear gas fired a day after some of worst violence in decades
* Street battle rages at Chinese University in New Territories
* Police say protesters have committed "insane" acts
* (Adds latest clashes, paragraphs 1, 9, 12, 15, 17)
By Clare Jim and Jessie Pang
HONG KONG, Nov 12 (Reuters) - Hong Kong police fired tear gas on Tuesday in the Central financial district, over the harbour in Mong Kok and at universities to break up pro-democracy protests which they said were leading the city to the "brink of total breakdown".
The clashes came a day after police shot a protester at close range and a man was doused with petrol and set on fire in some of the worst violence in the Chinese-ruled city in decades.
A flash mob of more than 1,000 protesters, many wearing office clothes and face masks, rallied in Central for a second day during lunch hour, blocking roads below some of the city's tallest skyscrapers and most expensive real estate.
After they had dispersed, police fired tear gas at the remaining protesters on old, narrow Pedder Street. Police made more than a dozen arrests, many pinned up on the pavement against the wall of luxury jeweller Tiffany & Co.
"Our society has been pushed to the brink of a total breakdown," a police spokesman told a briefing, referring to the last two days of violence in the former British colony.
He said masked "rioters" had committed "insane" acts, such as throwing trash, bicycles and other debris onto metro tracks and overhead power lines, paralysing the transport system.
He said the man set on fire on Monday was still in critical condition and appealed for information on who was responsible.
Police also fired tear gas at City University in Kowloon Tong, beneath the Lion Rock, and at Chinese University on the other side of the mountain, where protesters threw petrol bombs and bricks at police.
Protesters at City University had stockpiled bricks and petrol bombs on the bridges and other approaches and were making small devices with nails. They had overrun the campus and were smashing up the next-door Festival Walk shopping mall and setting fires.
Streets inside and outside the Chinese University campus entrance were littered with bricks, other debris and small street fires as police tackled some protesters to the ground.
A van used as part of a street barricade was set ablaze.
"IT'S OUR SCHOOL"
The students were taking part in a heated late-night exchange with the principal when clashes reignited, with police again firing volleys of tear gas and protesters throwing petrol bombs, lighting up the sky.
"It's crazy that police have been firing tear gas for more than 20 minutes. If they didn't come in, we wouldn't clash with them. It's our school. We need to protect our home," Candy, 20, a student, told Reuters earlier.
Several people were wounded, including a student reporter hit in the eye, apparently by a brick, who was sitting in tears as friends offered comfort.
Police also fired tear gas in the nearby new town of Tai Po and in the densely populated Kowloon district of Mong Kok, whose shopping artery Nathan Road has been the scene of many clashes.
Hong Kong leader Carrie Lam said protesters were being extremely selfish and hoped that universities and schools would urge students not to take part in the demonstrations.
More than 260 people were arrested on Monday, police said, bringing the total number to more than 3,000 since the protests escalated in June. Schools and universities said they would close again on Tuesday.
Protesters are angry about what they see as police brutality and meddling by Beijing in the freedoms guaranteed under the "one country, two systems" formula put in place when the territory returned to China from British rule in 1997.
China denies interfering and has blamed Western countries including Britain and the United States for stirring up trouble.
The United States on Monday condemned "unjustified use of deadly force" in Hong Kong and urged police and civilians alike to de-escalate the situation.
Chinese Foreign Ministry spokesman Geng Shuang urged Britain and the United States not to intrude, saying: "Hong Kong affairs are purely China's internal affairs that allow no foreign interference. We urge the United States, United Kingdom and other countries to earnestly respect China's sovereignty."
China has a garrison of up to 12,000 troops in Hong Kong who have kept to barracks since 1997 but it has vowed to crush any attempts at independence, a demand for a very small minority of protesters.
Geng also told a briefing in Beijing that China's government firmly supports Lam's administration and the Hong Kong police "in law enforcement, maintaining social order and protecting the safety of citizens".
Following Tuesday's violence, the Hong Kong Jockey Club said all off-course betting centres would be closed ahead of Wednesday's racing at Happy Valley, "to ensure the safety of our employees and customers".
The "Mark Six" lottery draw, originally scheduled for Tuesday night, was postponed until Thursday. (Reporting by Donny Kwok, Clare Jim, Marius Zaharia, Twinnie Siu, Clare Jim, Josh Smith, Kate Lamb, Jessie Pang and Farah Master in Hong Kong and Cate Cadell in Beijing; Writing by Anne Marie Roantree and Nick Macfie; Editing by Simon Cameron-Moore, Gerry Doyle and Catherine Evans)
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