Two crowd-control vehicles were dispatched after protesters earlier took control of a major road, where thousands stood behind barricades and shielded themselves from police tear gas with umbrellas.
The vehicles chased protesters for several hundred metres before they dispersed into surrounding side streets and a nearby mall.
Tseun Wan is best known for its tower-block housing estates and new office blocks, but on Sunday its streets descended into chaos as protesters threw a number of petrol bombs and bricks at riot police.
A police officer fired a gun into the air at around 8.00 p.m. (1200 GMT) after he was surrounded by eight to 10 protesters, according to a district council protest monitor.
The clashes were some of the most intense yet in Hong Kong since protests began on June 9 against a legislative bill that would have allowed for criminal extradition to mainland China, which has a separate legal system from Hong Kong.
Protesters braved the heat and smog on Saturday, only to march through intermittent heavy rains on Sunday.
As demonstrations enter their 12th week, protesters said they are still as determined as ever to protest against the government as they see themselves taking a last stand against political repression from China.
“It’s a last chance.
“I think the government’s control will be tighter and tighter and I don’t think they will let loose, so this could possibly be our last chance to fight,’’ said protester Phoenix Ip, who attended a police-sanctioned march through western Kowloon with her two-year-old son and husband.
“I’m pretty pessimistic about the future – but we still have to try.
“At least we tried for our next generation,’’ she said.
Hong Kong is a former British colony that returned to Chinese rule in 1997, and its unique identity and semi-autonomous status remain important rallying points for protesters.
Many believe the city has seen a decline in civil and political rights since the failure of the 2014 democracy protests known as the Umbrella Movement.
“China doesn’t want to lose Hong Kong, they want Hong Kong to become part of China and act like Chinese people who just follow what the government tells them,’’ said protester Chevron Hor.
“I don’t think anyone wants to see that happen.’’
While China is yet to signal whether it will intervene with its military or police in Hong Kong, Beijing has put renewed pressure on Hong Kong companies to condemn anti-government protests.
Earlier this week, the MTR Corporation, which runs Hong Kong’s subway system, received an injunction against protesters.
It said it may also suspend service without warning to stations where violent clashes occur.
Service at stations near Saturday and Sunday’s protests was also suspended.
The announcement follows commentary in Chinese state media accusing the MTR of colluding with protesters after extra trains were sent to help residents leave a violent protest in July.