Tens of thousands of pro-democracy protesters are blocking Hong Kong's streets, shutting down the territory's business hub and ignoring appeals to leave.
The demonstrations have spread to other areas including a shopping district and a heavily populated residential area.
Police said they used tear gas 87 times in clashes with protesters on Sunday.
On Monday, the government said riot police were being withdrawn as people had "mostly calmed down".
But some banks and schools were closed, and there was transport chaos.
Protesters - a mix of students and supporters of the Occupy Central pro-democracy movement - are angry at Beijing's plans to vet candidates for Hong Kong's 2017 leadership elections.
They want a free choice of candidates when they cast their ballots for the chief executive - something Beijing says is out of the question.
Sunday saw angry scenes and dozens of arrests on Hong Kong's streets as tens of thousands of protesters faced riot police in the heart of the city.
In a news conference on Monday, Cheung Tak-keung, assistant commissioner of police for operations, said police had used the "bare minimum force".
He said 41 people had been injured in the past three days, including police officers.
Some of the protesters remained camped out around the government complex overnight on Sunday, sleeping on the ground and some erecting barricades.
About 3,000 people have also blocked a major road across the bay in Mongkok, on the Kowloon peninsula, while a crowd of about 1,000 faced police in the busy shopping district of Causeway Bay, east of central Hong Kong.
Britain's Foreign Office said it was "concerned" about the situation in Hong Kong, and called for the right to protest to be protected.
"It is important for Hong Kong to preserve these rights and for Hong Kong people to exercise them within the law," it said in a statement.
The Hong Kong government has urged protesters to stay calm and leave peacefully.
But schools in three districts have been closed and the city remains heavily disrupted, with several major thoroughfares blocked.
One man said protesters were growing more confident. "Police don't have enough officers to close down the districts where there are protests," Ivan Yeung, 27, told AFP news agency.
Overnight, Hong Kong's chief executive reassured the public that rumours the Chinese army might intervene were untrue.
"I hope the public will keep calm. Don't be misled by the rumours," CY Leung said.
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