Tens of thousands of demonstrators have gathered for a peace rally in central Hong Kong, as the city's security chief furiously denied the government had used triad gangs to attack them a day earlier.

Huge crowds on Saturday moved into the main protest site in Admiralty, opposite the government headquarters, for a seventh night of a campaign for free elections, vowing to stand firm in the face of attacks on their ranks by aggressive counter-demonstrators.

"Democracy now! Democracy in Hong Kong!'' thousands chanted as speakers from the movement seeking political reforms urged them to persist.

Joshua Wong, a 17-year-old student leader, said: "We are not seeking revolution. We just want democracy," adding his movement did not want to see blood spilled.

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

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She added that there were rumours circulating that the government would take action soon and there have been calls for people to go back to work and their normal duties.

On Friday, Mong Kok and Causeway Bay descended into chaos as opponents to the rallies attacked protesters and tore down their tents and barricades.

There were claims among the crowds that hired thugs from triad criminal gangs had been hired to cause trouble. 

Police said several suspected triad members were among the 19 arrested after Friday's clashes, but the city's security chief denied allegations that the government had called on the services of paid thugs.

There were fresh clashes on Saturday in Mong Kok. Standoffs between the protesters and their antagonists grew uglier during the day, as the two sides traded insults and at times taunted police. 

Rights group Amnesty International reported a number of sex attacks and attacks on journalists, and said police "stood by and did nothing" to protect protesters.

Friday's violence prompted student leaders to scrap talks with the government - promised by the city's chief executive, Leung Chun-ying - removing hopes of a resolution to the crisis.

On Saturday Leung said talks were the only way forward. "There are many problems to be resolved in society, but the right way is through rational communication, not fighting on the streets," he said.

The Hong Kong Federation of Students, the main protest group, later said that it was willing to reopen talks if its conditions were met. The terms include a thorough police investigation into the events in Mong Kok and claims that police colluded with triad members.

Protesters demand the right to nominate who can run as their next leader in 2017 elections. Beijing insists only candidates it has approved will be able to stand.

Source: Al Jazeera and agencies