Hong Kong democracy protesters defied volleys of tear gas and police baton-charges to stand firm in the center of the global financial hub on Monday, one of the biggest political challenges for Beijing since the Tiananmen Square crackdown 25 years ago.
The unrest, the worst in Hong Kong since China resumed its rule over the former British colony in 1997, sent white clouds of gas wafting among the world's most valuable office towers and shopping malls as the city prepared to open for business.
Televised scenes of the chaos also made a deep impression on viewers outside Hong Kong, especially in Taiwan, which has full democracy but is considered by China as a renegade province which must one day be reunited with the Communist-run mainland.
The protests, led mostly by young tech-savvy students who have grown up with freedoms not enjoyed in mainland China, represent one of the biggest threats confronted by Beijing's Communist Party leadership since it launched a bloody crackdown on pro-democracy student protests in Tiananmen Square in 1989.
"Taiwan people are watching this closely," Taiwanese President Ma Ying-jeou said in an interview with Al Jazeera.
Read MoreImages of Hong Kong's violent weekend
China rules Hong Kong under a "one country, two systems" formula which accords the territory limited democracy. The protesters are demanding Beijing give them full democracy, with the freedom to nominate election candidates, but China recently announced that it would not go that far.
Organizers said as many as 80,000 people thronged the streets over the weekend, after the protests flared on Friday night. No independent estimate of crowd numbers was available.
Banks in Hong Kong, including HSBC, Citigroup, Bank of China, Standard Chartered and DBS, temporarily shut some branches and advised staff to work from home or go to secondary branches.
The Hong Kong Monetary Authority (HKMA), the city's de facto central bank, said it had activated business continuity plans, as had 17 banks affected by the protests.
The HKMA said the city's interbank markets and Currency Board mechanism, which maintains the exchange rate, would function normally on Monday. It said it stood ready to "inject liquidity into the banking system as and when necessary".
Read MoreHong Kong protests explained
Hong Kong witnessed extraordinary scenes at the weekend as thousands of protesters, some armed with nothing more than umbrellas, blocked the main road into the city and police responded with pepper spray, tear gas and baton charges.
Markets more or less took the weekend's unrest in their stride, proof yet again of the pre-eminent place trade has always taken in Hong Kong.
Hong Kong shares fell 2.3 percent.
Scuffles break out
Some protesters erected barricades to block security forces early on Monday, although a relative calm descended after dawn.
People placed discarded umbrellas over students sleeping in the sun, while others distributed water and masks to guard against tear gas and pepper spray.
Many roads leading to the Central business district remained sealed off as thousands defied police calls to retreat. In nearby Admiralty district, police removed a makeshift roadblock of railings, trash bins and bollards, only for student protesters to rebuild the barricade as soon as they moved on.
Commuters heading in to work stopped to take pictures.
Only hours earlier, police had baton-charged a crowd blocking a road into the main government district in defiance of official warnings that the demonstrations were illegal.
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Protesters called on Hong Kong leader Leung Chun-ying to step down. Several scuffles broke out between police in helmets, gas masks and riot gear, with demonstrators angered by the firing of tear gas.
"If today I don't stand up, I will hate myself in future," said taxi driver Edward Yeung, 55, as he swore at police. "Even if I get a criminal record it will be a glorious one."
Across Hong Kong's famed Victoria Harbour, smaller numbers of protesters, including some secondary school students, also gathered in the Mong Kok district of Kowloon.
"I didn't think too much (about democracy) but, because I am a Hong Konger, I just want to help as much as possible," said Ching Leung, 21, as she sat in her car. She said no one had asked her to join the protests and she wasn't afraid of police.
"I don't care, let them come."
Read MoreBad news in Hong Kong is good news for Singapore
Some of the younger students said they would return to classes on Monday afternoon.
In 1989, Beijing's bloody Tiananmen crackdown sent shock waves through through HongKong as people saw how far China's rulers would go to keep their grip on power.
Thousands of protesters still milled around the main Hong Kong government building on Monday, ignoring messages from student and pro-democracy leaders to retreat for fear that the police might fire rubber bullets.
Australia and Italy issued travel warnings for Hong Kong, urging their citizens to avoid protest sites. The U.S. State Department said in an email Washington supported Hong Kong's well-established traditions and fundamental freedoms, such as peaceful assembly and expression.
At the height of the clashes police, in some places lined five deep, used pepper spray against activists and shot tear gas into the air. The crowds fled several hundred metres, hurling abuse at police they called "cowards".
The "one country, two systems" formula guarantees Hong Kong a high degree of autonomy and freedoms not enjoyed in mainland China, with universal suffrage set as an eventual goal.
However, Beijing last month rejected demands for people to freely choose the city's next leader, prompting threats from activists to shut down the Central business district.
Read MoreInstagram blocked in China amid #OccupyCentral movement
China wants to limit 2017 elections to a handful of candidates loyal to Beijing. Communist Party leaders worry that calls for democracy could spread to cities on the mainland.
Hong Kong leader Leung had earlier pledged "resolute" action against the protest movement.
A spokesperson for China's Hong Kong and Macau Affairs Office said the central government fully supported Hong Kong's handling of the situation "in accordance with the law".
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Such dissent would never be tolerated on the mainland, where the phrase "Occupy Central" was blocked on Sunday on Weibo, China's version of Twitter.