Thousands of demonstrators have clashed with police in running scuffles in the district of Mong Kok in a bid to reclaim part of one of the largest and most volatile protest sites in Hong Kong.
Hundreds of riot police early on Saturday baton-charged the crowds with shields, pepper spraying and wrestling a string of protesters to the ground.
The protesters, some of whom pelted police with eggs and bottled water, retreated but regrouped swiftly in other spots.
Many rushed to lay fresh barricades across roads amid a wail of sirens and loud chants for "real full democracy".
The fresh tensions will be a setback for authorities who have struggled for months to find a resolution to the most serious governance crisis to be faced in the former British colony since it returned to Chinese rule in 1997. The protesters want the 2017 elections for a new leader to be fully democratic.
The protests have simmered for three consecutive nights in Mong Kok since police staged a swift clearance of the area's protest encampment on Wednesday, arresting more than a hundred people including key student leaders Joshua Wong and Lester Shum.
Amnesty International on Friday warned the police against the use of excessive force after Wong and Shum both said they were beaten during their arrests. Several reporters were also roughed up, prompting the Hong Kong Journalists Association to lodge a formal complaint and plan a protest.
"Is there a need to really use so much force to beat us," said Wong Ching-san, a young protester wearing a black jacket and flip flops. "We're not trying to cause violence but when they attack us we fight back."
Friday marks two months since police first fired tear gas to disperse demonstrators from the main protest site in the Admiralty district next to government offices in the heart of the Asian financial centre.
The protests, which have lasted well beyond many people's expectations, drew more than 100,000 on to the streets of Hong Kong at the peak.
While numbers have dwindled, they have swelled to several thousand at weekends and at key moments given a deep-rooted frustration at China and Hong Kong's refusal to in any way offer to meet their democratic demands.
China rules Hong Kong under a "one country, two systems" formula that accords the former British colony a degree of autonomy and freedoms not enjoyed in mainland China, with universal suffrage set as an eventual goal.