Officers returned fire with tear gas as they clashed with hundreds of protesters following a march against the government’s installation of “smart lampposts”, which are equipped with cameras and sensors.
The government has said the lampposts will only collect air quality, traffic and weather data, but protesters fear they could be used for surveillance.
Demonstrators armed with bamboo poles and baseball bats fought with officers wielding batons outside a police station and a nearby shopping mall.
Police fired tear gas to disperse the crowd after repeated warnings, the government said in a statement.
Earlier in the day, some protesters attacked a smart lamppost by using an electric saw to slice through the bottom of the post and pulling ropes to send it crashing to the ground.
The violence came after nearly two weeks of calm in Hong Kong, which saw a rare weekend without the firing of tear gas last week.
The semi-autonomous region has been gripped by protests since June, which began in opposition to an extradition bill with mainland China but have since become a broader pro-democracy movement.
Although the government has suspended the bill, which would have allowed Hong Kong residents to be sent to China to stand trial, protesters have called for it to be completely withdrawn.
In addition, they have expanded their demands to include free elections for the city’s top leader and an independent inquiry into alleged police brutality.
The protest march on Saturday started peacefully as supporters demanded the removal of the lampposts over fears that they could contain facial recognition software used for surveillance by Chinese authorities.
"Hong Kong people's private information is already being extradited to China. We have to be very concerned," organiser Ventus Lau said ahead of the march.
The government has said it plans to install about 400 of the lampposts in four urban districts.
Support free-thinking journalism and subscribe to Independent Minds
Hong Kong’s government-owned subway system operator, MTR Corporation, also shut down its stations and suspended train services near the march.
Adi Lau, the system’s operations director, described the conflict around the protests as “the biggest challenge that the MTR Corporation has experienced in its 40 years of operation”.
MTR was recently accused by Chinese state media of helping demonstrators escape police in previous protests.
Agencies contributed to this report