Eight people were jailed for up to 52 months on Friday and another was detained at a training centre over a protest in Tsim Sha Tsui on August 11, 2019.
Two of them admitted taking part in a riot and seven were found guilty of the charge. A tenth person was acquitted.
One of the defendants was also found guilty of possessing firearms or ammunition without a licence after being found with nine used tear gas canisters.
District Court judge Lily Wong said up to 1,000 people had gathered in the streets of Tsim Sha Tsui, bringing traffic to a standstill and causing a disturbance to the public. Some protesters threw petrol bombs at a police station, injuring an officer's leg, and blocked the station's entrance with bricks and water barriers.
But Wong said there was no evidence that the defendants had been violent or played leading roles in the protest. She said they had come prepared to cause trouble, however, since they wore black clothes.
The pair who pleaded guilty to rioting were given 40 and 42 months in prison respectively, and six of those who denied the charge were sentenced to between 50 and 52 months behind bars.
A 17-year-old student was sent to a training centre.