Fresh scuffles broke out on Saturday between Hong Kong pro-democracy protesters and opponents of the week-long demonstrations, reigniting concerns that the Chinese-controlled city's worst unrest in decades could take a violent turn.
The protests have been largely peaceful since police last Sunday fired tear gas at crowds demanding Beijing grant Hong Kong the unfettered right to choose its own leader. But the mood turned ugly on Friday at the most volatile protest site, in the teeming suburb of Mong Kok where some criminal gangs are suspected to be based.
Police intervened to prevent a violent escalation, but a rowdy crowd of around 2,000 filled a major intersection in the small hours of Saturday and the atmosphere was highly charged as police in riot gear tried to keep them under control.
Witnesses said about a thousand protesters faced off in Mong Kok at mid-morning on Saturday, although there were no uniformed police in sight.
Pro-democracy activists vowed to hold their ground through the weekend. "We will retreat after that if the situation gets worse, such as if mobs start flashing their knives at us," said Daniel Tang, who is in his 30s.
Student activists, established protest groups and ordinary Hong Kongers have joined forces to present Beijing with one of its biggest political challenges since it violently crushed pro-democracy protests in and around Tiananmen Square in 1989.
Tens of thousands of protesters have staged sit-ins across Hong Kong over the past week, demanding the city's pro-Beijing leader Leung Chun-ying step down and China reverse a decision in August to handpick the candidates for a 2017 election.
Police said they had arrested 19 men since Friday, with local state-owned broadcaster RTHK saying eight of them were suspected members of Triads, or Chinese criminal gangs. Eighteen people were injured, including six police officers, according to the RTHK report.
One of the main student groups behind the "Occupy Central" protest movement said it would pull out of planned talks with the Hong Kong government, because it believed authorities had colluded in the attacks on demonstrators in Mong Kok.
"The government and police today connived in the attack by Triads ... on peaceful occupiers, so they have shut the way to dialogue and must bear the consequences," the Hong Kong Federation of Students said in a strongly worded statement.
The notorious Triads operate bars, nightclubs and massage parlours across Mong Kok, an area of high-rise apartment blocks across the harbour from the main protest areas.
Witnesses said anti-Triad police wearing trademark black vests were active in the area on Friday.
At times over the past week, police have left the streets, saying they wanted to ease tensions, though the reason for their apparent absence from this scene on Saturday morning was unclear.
Police have defended their handling of fighting in the area, saying they had exercised "dignity and restraint and tried our best to keep the situation under control".
But Amnesty International issued a statement criticising them for "(failing) in their duty to protect hundreds of peaceful pro-democracy protesters from attacks by counter demonstrators."