Hong Kong police cleared activists from one of the largest protest sites in the city on Wednesday and arrested Joshua Wong and Lester Shum, two of the student leaders at the heart of the pro-democracy movement that has shaken the Asian financial hub.

Scuffles broke out when riot police moved against hundreds of protesters on Nathan Road, in the gritty Mong Kok district, following clashes overnight, Reuters witnesses said.

"You can't defeat the protesters' hearts!" screamed Liu Yuk-lin, a 52-year-old protester in a hard hat holding a yellow umbrella, the symbol of the movement, as she stood before lines of police in helmets and goggles.

"It's not the end. We still have plan B; either to occupy other places or to step up our actions. - Helen Lau, student protester

But there was no serious violence, and after about three hours the operation was complete and traffic was flowing through as area where demonstrators had camped out since late September to call for greater democracy in the former British colony.

Mong Kok has been a flashpoint for clashes between students and mobs intent on breaking up the protests, which have posed one of the biggest challenges to China's Communist Party leaders since the crushing of student-led pro-democracy demonstrations in Beijing in 1989.

Crowds cheer removal

Crowds nearby cheered and clapped as the final protesters were removed from the site on Wednesday.

Earlier, court-appointed bailiffs had warned protesters to leave and around 80 workers in red caps and "I love Hong Kong" T-shirts began clearing metal and wooden barricades laid across Nathan Road, where hundreds of tents had been erected in a two-month civil disobedience campaign.

Police officers remove tents erected by pro-democracy protesters in the Mong Kok district on Wednesday in Hong Kong. The Mong Kok protest site is scheduled for clearance by bailiffs this week after Hong Kong's high court authorized police to arrest protesters. (Lam Yik Fei/Getty Images)

They had been met by hundreds of protesters brandishing yellow banners and chanting for "full democracy".

"If you resist you face possible imprisonment. We warn you to immediately stop resisting," said a policeman into a loudspeaker before jeering activists.

Several protesters who resisted were hauled away, witnesses said. Hong Kong's Cable TV said 4,000 police were involved.

A Reuters witness saw police take away Shum, and the Facebook page of the student group Scholarism announced that Wong had been arrested for contempt of court.

Although the protests have had no formal leadership structure, Wong and Shum were part of a group of students who many looked to as the movement's de facto leaders.

Move could trigger retaliatory protests

The clearance of the Mong Kok site is a big breakthrough in the authorities' efforts to end the most tenacious protest movement in Hong Kong's recent history, although it could trigger retaliatory protests elsewhere as the activists regroup.

"It's not the end," said Helen Lau, a young activist with a leather yellow ribbon around her neck, who was shouting at police and demanding to re-enter the cleared area. "We still have plan B; either to occupy other places or to step up our actions."

Policemen walk along an empty Nathan Road after taking down tents and barricades set up by pro-democracy protesters at Mong Kok shopping district. (Bobby Yip/Reuters)

Protesters still occupy segments of roads, blocking traffic, in the city's Admiralty district near government offices and Causeway Bay, a major shopping area.

It was not clear if or when police might try to clear the remaining protest sites.

Overnight, police had arrested 80 protesters in running clashes in Mong Kok following the clearance of part of a nearby street the previous day.

The crowded, working class district has been the scene of some of the most violent confrontations in the two-month long "Occupy Central" civil disobedience campaign.

The pro-democracy movement is showing signs of splintering, with radical voices calling for escalated action after nearly two months of stalemate in their campaign for full democracy.

In August, Beijing offered the people of Hong Kong, which reverted to Chinese rule in 1997, the chance to vote for their own leader in 2017, but said only two to three candidates could run after getting majority backing from a 1,200-person "nominating committee" stacked with Beijing loyalists.

More than 100,000 people took to the streets at the peak of the protests, but numbers have dropped to a few hundred scattered in tents over three main sites.