More than a thousand rival protesters, some wearing helmets, faced off in a densely populated, gritty district of Hong Kong on Saturday, fueling concerns that the city's worst unrest in decades could take a more violent turn.

After a night of trouble that resulted in 19 arrests, supporters of the city's pro-Beijing government rallied next to pro-democracy protesters in Mong Kok, a working class neighborhood near the popular shopping district of Tsim Tsa Shui.

Many Hong Kong residents expressed anger and frustration at police handling of the unrest, with some accusing security forces of cooperating with criminal gangs, failing to make arrests and helping some attackers to exit the scene quickly.