The weekend's demonstrations follow a week of student-led boycotts and protests against what many see as the encroachment of China's political will on Hong Kong's governance, in the face of China's decision to only allow Beijing-vetted candidates to stand in the city's elections for chief executive, Hong Kong's top civil position.
Thousands remain at the protest site at government buildings in Hong Kong's business district. Police have indicated that the site will be cleared shortly.
While the protests -- which have swelled following two consecutive nights of "occupation" of government property -- have been largely peaceful, police say they have made dozens of arrests. Those taken into custody range in age from 16 to 58.
Pepper spray has been used, along with tear gas being deployed against more than one group of protesters around the Central Government Offices. Riot police have also wielded batons against protesters. CNN teams witnessed police donning riot gear and gas masks.
Emergency personnel have been deployed to the front line of the clashes.
The city's chief administrator, Chief Executive C.Y. Leung, said at a news conference Sunday afternoon that the Hong Kong Special Administrative Region government is "resolute in opposing the unlawful occupation" of the government buildings.
"The police are determined to handle the situation appropriately in accordance with the law," he said.
Protest organizers announced early Sunday evening that demonstrators have occupied the upscale Pacific Place shopping mall, located near the main protest site. They said that numbers of protesters continue to grow.
Leung, who was addressing the protesters for the first time, urged Hong Kong's residents to express their dissatisfaction with the political process in a safe and lawful manner.
He said that a round of consultations on electoral reform will take place "shortly" but went on to appeal to pro-democracy activists to engage in rational discussions through lawful means "so as to allow the more than 5 million eligible voters in Hong Kong to elect the chief executive in 2017 for the first time in Hong Kong's history by one person, one vote." He reaffirmed that the government in Hong Kong will uphold Beijing's decision.
The Chinese central government said that it is "confident" that the Hong Kong government can handle the movement lawfully,according to a report in Chinese state media. The Chinese government opposes all illegal activities that "could undermine rule of law and jeopardize 'social tranquility,'" the report says.
Yvonne Leung, the spokeswoman for the Hong Kong Federation of Students, which organized the protest, told CNN that the demonstrators plan to continue to occupy the area outside Hong Kong government headquarters in an act of civil disobedience.
In a statement Sunday evening, she said the protesters called for the chief executive and three other politicians working on political reform to resign. If the demand, and three others, go unmet, the students vowed to step up their protests and will boycott school.
Yvonne Leung said the group has not received any news concerning the whereabouts of Hong Kong protest leaders Alex Chow and Lester Shum, who were arrested on Saturday. High school student protest leader Joshua Wong is still under detention.
The previous week had seen days of action, as university and high school students came out in droves to rally against what they believe is the Chinese central government's reneging on key promises for Hong Kong's political future.
Student protesters joined
Since then, the movement has developed into a much larger, more inclusive display of defiance as the Occupy Central movement joined the students' rally.
The pro-democracy advocacy group -- it is unaffiliated with the broader anti-capitalist Occupy movement -- has been vowing to lead a campaign of civil disobedience in the face of China's decision to control what candidates can run for Hong Kong's top office.
"Occupy Central has formally begun," said a statement by the group, released in the early hours of Sunday morning.
"The two nights of occupation of Civic Square in Admiralty have completely embodied the awakening of Hong Kong people's desire to decide their own lives," the statement said.
"The courage of the students and members of the public in their spontaneous decision to stay has touched many Hong Kong people. Yet, the government has remained unmoved. As the wheel of time has reached this point, we have decided to arise and act."
The movement will continue the current protest, the statement said, using the student-led occupation of the Central Government Office as a starting point.
Occupy Central leader Benny Tai and pro-democracy legislators Lee Cheuk-yan and Leung Kwok-hung were spotted at the protest site Sunday.
Government: Fears are 'unfounded'
Leung, the city's chief executive, told CNN that fears that the nominating process for the 2017 election were too restrictive were "unfounded."
"We have not even started to discuss the detailed but crucial aspects of the nominating process for potential chief executive candidates," he wrote in an exclusive commentary.
"This will be the subject of a public consultation to be launched soon and which will eventually lead to the enabling legislation on changes to the electoral method for the 2017 election."
Organizers said some 60,000 protesters turned out for a Saturday night rally and police tried to block them from joining the protesters who are part of a sit-in outside the government complex.
Sunday saw an increased police presence at the protest site. At the entrance of the protest area, around 30 officers formed a cordon between the main group of protesters, fenced inside the complex's Civic Square area inside the premises, and several smaller gatherings.
Those on the outside of the fences, wearing goggles or masks and raincoats, and holding umbrellas to protect against the possible use of pepper spray, chanted: "Let us through."
As the day wore on, the protest remained calm, with marshals telling the crowd not to provoke police, while also urging the authorities not to use excess force.
Core group of protesters isolated
The three entrances to Civic Square, which houses a core group of protesters, were blocked off by steel fences and guarded by around 100 police officers.
A protest leader, over a public address system, told the crowd that since the police claim the gathering is an unlawful assembly, supplies including water and audio equipment won't be allowed into the sealed-off protest area. Supplies, the voice on the microphone said, were also confiscated by the police.
Demonstrators claimed that undercover officers had joined the main protest group, and others said they had seen police preparing water cannon.
Many in the city, which under British rule enjoyed considerable political freedom, fear a rollback of the city's political autonomy, agreed between Britain and China under the Basic Law. The Basic Law, which serves as a de facto constitution, was written in the lead-up to the 1997 handover of sovereignty.
Amnesty International issued a statement condemning the arrests and violence used against student protesters.
"The police response to events on Friday night is a disturbing sign that the Hong Kong authorities will take a tough stance against any peaceful protest blocking the financial district," said Mabel Au, director of Amnesty International Hong Kong.
"The quick use of pepper spray, deployment of riot police in full gear and arrests at government headquarters does not bode well for the potentially massive protests expected this week. All those being held solely for exercising their rights to freedom of expression and assembly must be immediately and unconditionally released."
As their ranks swell and the students' movement is assimilated into the wider pro-democracy movement, their political vision remains clear.
"The future of Hong Kong is ours," said 16-year-old student Phoebe Leung. "I can't change Hong Kong, but if all of us are here ... we may change Hong Kong's future."