Hong Kong protest leaders have called off talks with the government following what they said were "organised attacks" on their supporters.

The Hong Kong Federation of Students made the announcement to boycott the talks aimed at ending week-old demonstrations after crowds descended on two of their camps on Friday, tearing down their tents and barricades. Student leaders said the attacks were orchestrated by paid people from "triad" criminal gangs.

"There is no other option but to call off talks," the students said in a statement.

"Everybody saw what happened today," they added. "The government and police turned a blind eye to violent acts by the triads targeting peaceful Occupy protesters."

Earlier, the three main protest groups issued a statement calling for the government to step in.

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

The secretary for security, Lai Tung Kwok, said the accusation of police cooperating with triad members or allowing triad activities during the protest was fabrication.

Of 19 people arrested on Friday, eight were said to have links to the triads.

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 the shopping district Mong Kok after they started to 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.

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.

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

Reporter's Diary - Al Jazeera's Divya Gopalan

One of the main student groups have told me that they are trying to move the focus of the protest back to Admiralty and Central areas of Hong Kong.

They are dismayed by what has happened in Mong Kok, and feel that the protests have taken a wrong turn.

They say the government and security have let them down and feel it is the government that has instigated the backlash, while security officials have done little to control the situation.

So their plan tomorrow is to try bring the protests back to these areas. Demonstrators are expected to gather again tonight.

The atmosphere is different from previous nights. It is more serious with groups chanting, and they are even more united than ever.

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