Hong Kong protest leaders have threatened to boycott talks with the government unless "organised attacks" on supporters stop, as clashes broke out at previously peaceful demonstrations.

The three main protest groups issued a statement late on Friday calling for the government to step in.

"If the government does not immediately prevent the organised attacks on supporters of the Occupy movement, the students will call off dialogue on political reform with the government," they said.

Notes from the field - Al Jazeera's Adrian Brown
Hong Kong's shopping district, Mong Kok, where the clashes happened is the heartland of the notorious triad underworld. And within the seething melee you can see heavily tattooed men giving orders. Some of those I spoke to, including Amy Yu, were angry with the students and the Occupy movement. She said she had enough and just wanted her life to get back to normal. Bennie Tai, a protest leader of the Occupy movement visited the scene and warned the planned talks with the government won't happen unless the police do more to protect the student groups. The mood is certainly darkening and we may be witnessing the start of a backlash. And Mong Kok could be where it begins.
Follow Adrian Brown on Twitter: @ajabrown

Opposition groups clashed with the protesters in one of Hong Kong's busiest shopping districts, Mong Kok, with the activists saying they believed the violence had been orchestrated by hired hands.

Talks had been promised by Hong Kong's Chief Executive Leung Chun-ying, who is under pressure from protesters to resign as they demand democratic reforms, but there was no sign on Friday that they had begun.

Thousands of people crowded the streets as demonstrators faced off against a group of anti-protesters in shopping district Mong Kok after they started to dismantle barricades, storm tents and rip down banners in an apparent backlash against the protests.

Al Jazeera's Adrian Brown, reporting from the scene in Mong Kok, said that he witnessed several violent skirmishes.

"At least two people, including an elderly man, were carried away by ambulance crews after crowds created a corridor to allow them to leave," he said. "I have also heard Mandarin being spoken, which suggests darker forces may be at work."

Police tried to hold back angry demonstrators who surrounded the protesters at a junction they had been occupying for five days.

One small group chanted "I want genuine democracy", while a crowd yelled at them to "Go home!" as police struggled to contain the confrontation.

"I don't support Occupy Central. We have to work and make money. Occupy is just a game," said a construction worker who gave his name as Mr Lee.

"Give us Mong Kok back, we Hong Kongers need to eat!" yelled another man removing the barricades there.

Police urged all sides to "stay calm and exercise restraint" in what they described in a statement as a "chaotic situation" in Mong Kok.

In a brief video, Leung appealed for an end to the Mong Kok protests and for both sides to go home. He again appealed for calm in the city.

There were also confrontations in the busy commercial district of Causeway Bay.

(For more photos from the scene of the clashes in Causeway Bay, visit our Live Blog)

One anti-protester there yelled: "This is not democracy, we need to feed our kids". Spectators cheered barricades being taken away.

Source: Al Jazeera and agencies