A deadline for protesters to clear Hong Kong's streets is just hours away, as the territory's Beijing-backed leader claimed the disorder risked "serious consequences" for public safety.

Chief Executive Leung Chun-ying said late on Saturday that the government was determined to "take all necessary actions to restore social order" and allow residents to "return to their normal work and life".

He said government staff needed to resume work by Monday morning, and set the deadline for protesters to disperse.

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Protesters, calling for universal suffrage, have camped out in several commercial districts of the city, blocking roads and access to government offices.

A meeting between the Hong Kong student federation, which is leading the protests, and a government representative on Sunday evening failed to reach an agreement on starting formal talks between protesters and the executive.

Crowds had thinned out by Sunday afternoon in the Admiralty district near the government's headquarters, hours after tens of thousands staged the biggest gathering yet of the week-long protest.

Principals from universities have called on students and teachers who have been protesting to come back to classes.

Leung issued an ominous warning about what would happen if the protests were not ended and streets near the government offices cleared.

"The situation may probably evolve into a state beyond control, and will have serious consequences to public safety and social order," he said.

Fresh clashes broke out on Sunday morning, with riot police using batons and pepper spray to fight back demonstrators.

Sunday marked exactly a week since police fired tear gas on protesters in an effort to disperse them, but only adding sympathy to their cause and boosting numbers.

The latest skirmishes erupted in the commercial district of Mong Kok, away from Admiralty where tens of thousands had gathered for a peace rally, singing democracy anthems.

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Al Jazeera's Divya Gopalan, reporting from Admiralty, said student leaders emphasised the need for the protest movement to remain peaceful and "not give the government any reason to break it up".

Mervyn, a 28-year-old sea-farer who came from Singapore to support the protests, said Hong Kongers had seen popular uprisings elsewhere in the world turn violent and were determined to keep protests peaceful.

"They watched the Arab Spring unfold. We are a peace-loving crowd here - we don't want the violence seen elsewhere."

He told Al Jazeera that the demonstrations had reached a stalemate, but the demonstrators were "not going to budge... We'll see who tires first!"

The protesters are demanding the right to nominate who can run as Hong Kong's next leader in 2017 elections.

The Chinese government, which regained sovereignty over Hong Kong from Britain in 1997, insists that only pre-approved candidates will be able to stand and has repeatedly said the protests are doomed to fail.

Source: Al Jazeera and agencies