A group of hardcore protesters threw petrol bombs at a police station as violence flared in Hong Kong during a banned march that drew thousands.
Authorities refused permission for a march through an upmarket shopping area, citing public order concerns.
But large numbers defied authorities, with a small group of black-clad protesters attacking a police station.
Hong Kong has been convulsed by pro-democracy protests for more than four months.
The unrest in the territory, which is part of China but enjoys unique freedoms, has been the worst crisis since the British handover in 1997.
At the Tsim Sha Tsui police station, officers fired tear gas as the building's gate was set on fire, before deploying a water cannon to clear the area.
Elsewhere, shops and Chinese banks were vandalised.
Not all of Sunday's demonstrators engaged in violence. Although the rally was illegal, it began peacefully.
What caused Sunday's clashes?
The anger of the crowd was partly fuelled by an attack on pro-democracy leader Jimmy Sham earlier this week which left him in hospital. He was set upon by five men with hammers in the Mong Kok district of Kowloon.
On Saturday, another man who was reportedly handing out pro-democracy flyers was stabbed.
Numbers attending protests have dropped from their peak. The movement has seen hundreds of thousands taking part in demonstrations on several occasions.
"The government are now refusing to authorise any peaceful protest," a demonstrator named Avery said on Sunday. "That means anyone who comes out will inherently be breaking the law. So that's the tactic the Hong Kong government is using."
Is there any solution in sight?
Originally, the protests were prompted by outrage at a new law that would have allowed criminal suspects to be extradited to mainland China.
People in Hong Kong are fiercely protective of their legal system and enhanced personal rights, which are governed under an arrangement known as "one country, two systems".
But they have grown increasingly concerned that China seeks greater control.
The extradition bill was eventually scrapped but the protest movement has broadened to include four other demands:
- For the protests not to be characterised as a "riot"
- Amnesty for arrested protesters
- An independent inquiry into alleged police brutality
- Implementation of complete universal suffrage
Hong Kong's embattled leader Carrie Lam is seen by many pro-democracy campaigners as a mouthpiece for Beijing – something she fiercely denies.