Hundreds of masked protesters used bins and ticket machines as barricades against riot police late Wednesday at a flashpoint Hong Kong metro station, where they earlier marked one month since a mob attack by suspected triad gang members.
That assault on July 21 had pushed the city deeper into political violence, but the sit-in on Wednesday was largely peaceful until police vans arrived at the Yuen Long station close to the Chinese border and the atmosphere soured.
Some protesters put on hard hats and gas masks, while others sprayed fire extinguishers and poured detergent, beer and oil on the concourse to impede entry by the police who had massed outside.
The demonstration was convened to mark a month since a gang wearing white T-shirts and armed with poles and sticks set upon anti-government protesters - unarmed and dressed in black - at the metro station.
The attack left nearly 50 people - including passers-by - in hospital, some with horrific wounds.
Hong Kong's police were heavily criticised for being slow to respond, fuelling rumours of collusion.
Police denied any links to the attack, but trust in the force - which was already facing an unprecedented challenge on the streets -- has since sunk to a nadir.
"People are here to tell the government that we are angry and we think that we need a fair judgment on the attackers," 23-year-old tutor Chloe told AFP, giving one name like many of the demonstrators.
Hong Kong's political crisis was spurred by an attempt to bundle through a bill allowing extradition to China through parliament.
But protests have billowed out into a wider pro-democracy movement, which has seen the financial centre's airport closed, violent street clashes with police and million-strong peaceful marches through city streets.
It is unclear in which direction the protests, which are leaderless and organised on social media, are heading after nearly three months of draining street action.
The city has enjoyed several peaceful protests recently -- without police baton charges, tear gas or protesters hurling rocks.
Hong Kong's government has so far refused to buck to any of their demands, including scrapping the extradition bill completely, the resignation of city leader Carrie Lam and a full independent inquiry into police actions during the protests.
But they say they are digging in for the long haul.
"Although we are so tired, we know that the momentum for the protests is still there," said a sit-in participant who identified himself only as Leung.
Hong Kong police on Tuesday said they had arrested 28 people over the July 21 incident.
Yuen Long is in Hong Kong's New Territories, a rural area where many of the surrounding villages are known for triad connections and their staunch support for the pro-Beijing establishment.
The demonstration was convened to mark a month since a gang wearing white T-shirts and armed with poles and sticks set upon anti-government protesters.