At least 48 police personnel were injured in violent clashes when authorities tried to remove illegal street stalls set up for Lunar New Year celebrations.
Of the 300 or so rioters, 24 were arrested, Xinhua news agency reported.
The riots erupted after a handful of illegal street vendors refused to halt business on Mong Kok, a busy commercial district, and clashed with law enforcement officials Monday night.
Rioters then attacked them with bricks, stones and other weapons. Police fired two warning shots in a bid to rescue their personnel. The violence was reported on Tuesday morning too.