Hundreds of people have again gathered at protest sites in Hong Kong, a day after demonstrators calling for general suffrage were attacked and accused police of not doing enough to stop the violence.

Demonstrators alleged that Friday's violence was orchestrated by paid thugs to stir up trouble and discredit the movement.

Rights group Amnesty International also blasted police, saying officers "stood by and did nothing" to protect protesters, whose rallies have led to much of the city grinding to a standstill for the past week.

Distrust of police has built up since officers used pepper spray and tear gas to disperse protesters occupying government buildings earlier this week. Police did form lines between the rival sides on Friday, and escorted some protesters to safety, but this was not enough to stop the violence.

Al Jazeera's Adrian Brown, reporting from the shopping district of Mong Kok, where the worst confrontations happened on Friday night, said the situation there was tense on Saturday, but shops were still open and business was going on as usual.

"Today the confrontations have been mostly verbal," he said. "But the skirmishes seem to ebb and flow and most of the violence tends to happen in the evening."

He said students had been reinforcing their barricades in the morning, with their opponents trying to take them down.

Talks called off

Reacting to Friday's attacks, protest leaders called off talks promised by Hong Kong's Chief Executive Leung Chun-ying, who is under pressure from protesters to resign, before the dialogue meetings had even started.

The Hong Kong Federation of Students made the announcement to boycott the talks 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.

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

Occupy Central says it is a pro-democracy movement and it has been spearheading the week-long protests alongside students. At the peak of the protests, thousands of people gathered in the business district, Central.

At a press briefing on Saturday, police denied acting in concert with triads, adding that 12 people had been injured, including six officers.

"Police in the small hours in different locations arrested 19 males," senior superintendent Patrick Kwok said.

"Within the people who were arrested, eight were arrested for illegal assembly. We believe these have triad backgrounds," Kwok said.

Triad gangs have traditionally been involved in drug-running, prostitution and extortion but are increasingly involved in legitimate ventures such as property and the finance industry.

Some are believed to also have links with the political establishment and previously there have been allegations of triads sending paid thugs to stir up trouble during protests.

'One-sided violence'

Geoff Crothall, the communications director at the China Labour Bulletin, an NGO defending workers' rights, said "whether or not these triads, these hired thugs, were acting under the organisation of the government or Beijing is not really the point".

Field Notes:

Adrian Brown, Mong Kok The triads are Hong Kong's most feared criminal group and Mongkok is their heartland. The district is notorious for prostitution and illegal gambling dens - all of which the triads' control. And so they have a vested interest in business returning to normal. They are also fiercely patriotic to the motherland. Were the triads out stirring up trouble on Friday? Well, I certainly saw heavily tattooed men (tattoos are a Triad signature) in the thick of last night's melee. I also heard people talking Mandarin, the predominant dialect on mainland China. Evidence, perhaps, of dark forces at work. Yet despite the violence and the simmering tensions today, I have not seen one broken shop window, one torched car and no looting. Many of these students may be breaking laws for the first time, but they remain respectful of most of them.

"What we need to understand is that all the violence is coming from one direction. Journalists and bystanders are not being attacked by pro-democracy protesters. All the violence comes from these anti-Occupy thugs and hooligans," he told Al Jazeera.

Some business owners and residents have been angered by the protests that have led to traffic diversions and other disruptions.

"The fight for democracy does not give you the right to occupy our streets and disturb us. We all have a mortgage to pay and need to make a living," a Mong Kok resident told Al Jazeera.

Crothall said some of the anti-Occupy protesters were undoubtedly local residents annoyed with disruptions caused by protests. But he stressed that the atmosphere around the Mong Kok protests site was mostly quiet and peaceful.

"There's not really a great deal of inconvenience being cause by the pro-democracy camp. There's clearly more to it than simply inconvenience."

Online, activists circulated videos of protesters in vain asking police to intervene to stop attacks.

Amnesty International said female protesters were being targeted with sexual assaults and harassment.

"Women and girls were among those targeted, including incidents of sexual assault, harassment and intimidation" in Mong Kok and Causeway Bay, another shopping district, the group said.

China rules the former British colony through a "one country, two systems" formula underpinned by the Basic Law, which accords Hong Kong some autonomy and freedoms not enjoyed on the mainland and has universal suffrage as an eventual goal.

But Beijing decreed on August 31 it would vet candidates who want to run for chief executive at an election in 2017, angering democracy activists, who took to the streets.