Riot police used tear gas throughout the afternoon and evening in Yuen Long, a town close to the border, after tense standoffs with protesters, some of whom were throwing projectiles and had surrounded a police van.
Hospital authorities said nine people were injured, with five in a serious condition.
Rubber bullets were fired later in the evening to disperse remaining protesters. Battles then broke out in the town's station as officers with batons and shields swooped on demonstrators there and made multiple arrests, leaving pools of blood on the floor.
Public anger has been raging since last Sunday when a gang of men in white T-shirts, armed with poles and batons, set upon anti-government protesters and bystanders in the same station in Yuen Long.
That brazen assault -- which hospitalised at least 45 people -- was an escalation of seven weeks of unprecedented political violence that shows little sign of abating as the city's pro-Beijing leaders refuse to budge.
Police have been heavily criticised for being too slow to respond to Sunday's violence, fueling accusations of collusion or turning a blind eye to the pro-government mob -- allegations the force has denied.
- Triad links -
Hong Kong has been plunged into its worst crisis in recent history after millions of demonstrators took to the streets and sporadic violent confrontations erupted between police and pockets of hardcore protesters.
The demonstrations were triggered by a controversial bill which would have allowed extraditions to mainland China, but have evolved into a call for wider democratic reforms and a halt to sliding freedoms.
Saturday's violence compounds the political crisis with the city's leadership seemingly unable, or unwilling, to end the chaos.
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.
Police say they have arrested 12 people so far in connection with Sunday's violence, nine of whom have known triad links.
The white shirt mob ran into two villages near Yuen Long station after their attack and later left without police making any arrests despite a large presence of officers.
These two villages became the focus of protester anger on Saturday.
The rally began peacefully. But small groups of more hardcore protesters, many in helmets and carrying shields, confronted police outside the villages and accused them of protecting triads.
Tensions quickly rose with projectiles hurled. Soon tear gas rounds were arcing through the air and a now-familiar pattern of running battles between police and protesters began.
On one road, a parked Lexus that was found to have wooden sticks and clubs similar to those used in Sunday's attacks inside it -- as well as a Samurai-style sword -- had been trashed.
By late evening only some 200 protesters remained around the main station who were then charged by riot police.
- Pokemon Go and shopping sprees -
In a rare move, police banned Saturday's rally saying they feared reprisal attacks against villagers from protesters, a decision that only heightened anger towards a force already perceived to be protecting pro-government aggressors.
Social messaging channels used to organise the largely leaderless movement filled with calls for people to go on a "shopping spree" in Yuen Long or play the popular mobile game Pokemon Go there.
One female protester surnamed Cheung said she wanted to show "we are not afraid and that Hong Kongers won't cower in fear".
"The police and (the government) are together suppressing people's freedom to express their views," she added.
- Few concessions -
Weeks of unprecedented protests with huge turnouts -- as well as frequent clashes and the sacking of parliament -- have had little luck persuading Beijing or Hong Kong's leaders.
Beijing has issued increasingly shrill condemnations in the last fortnight, but has left it to the city's semi-autonomous government to deal with the situation.
City leader Carrie Lam has shown no sign of backing down beyond agreeing to suspend the extradition bill.
On Friday thousands held a 10-hour protest at the airport arrival hall in a bid to "educate" visitors about their movement -- especially those on the Chinese mainland where news is heavily censored.
The protest was peaceful and there was no disruption to flights.
Protesters also plan to march on Sunday through a district where riot police fired tear gas and rubber bullets at projectile-hurling protesters the week before.
Riot police used tear gas throughout the afternoon and evening in Yuen Long, a town close to the border, after tense standoffs with protesters, some of whom were throwing projectiles and had surrounded a police van