Dozens of masked men rushed barricades at Hong Kong's main pro-democracy site on Monday, triggering clashes as demonstrators tried to push them back and police struggled to contain the chaos.
Groups of men, many wearing surgical masks, descended on the front lines of the rally at Admiralty near Hong Kong's central business district, hours after police had moved in to remove some barricades and shrink the site.
Two of the men were tackled to the ground by police, who also formed a cordon around the masked group.
Protesters, who have come under attack from organised crime gangs known as triads at another flashpoint rally site in Mongkok, shouted: "Weapons! Weapons!" and "Arrest the triads".
Television footage showed one masked man being forced to drop a small flick-knife.
Taxi drivers, many of whom have voiced frustration with more than two weeks of protests which have blocked roads and caused traffic gridlock, added to the fray by converging on the site in their cars, beeping horns and shouting at demonstrators.
Some had "We can't take it any more" printed on the fronts of their cabs.
Other groups opposed to the "Occupy" pro-democracy campaign also appeared at Admiralty, chanting "Occupy is illegal" and demanding that roads be reopened.
Police formed a line in front of the anti-Occupy protesters as trucks with cranes arrived on the scene and began removing barricades, an AFP photographer saw.