The clashes broke out after police moved in to clear"hawkers", or illegal vendors who sell local delicacies,trinkets and household goods from makeshift streetside stalls.
The hawkers, long a common sight on Hong Kong’s bustling streets, quickly attracted a strong social media following underthe hashtag #FishballRevolution.
"To ensure public safety and public order, police took resolute actions, including using baton and pepper spray, to stop the unlawful violent acts," police said in a statement.
The protesters had dispersed by 0000 GMT. More than 100 confronted police in a tense stand-off hours before on the Chinese New Year holiday, when most of the city is shut down, with rubbish bins and flower pots in flames nearby.
Police told Reuters they were awaiting orders about securityplans for Tuesday night.
Paul Lee, a 65-year-old security guard, said: "This is not the first time there has been violence in Mong Kok."
"I am deeply disappointed in the government," he said.
The underground train station for Mong Kok, a bustling shopping district packed with street markets, shops and high-rise residential buildings, was closed temporarily.
A police statement said three men aged 27 to 35 were arrested for assaulting a police officer and obstructing police,while three police officers received hospital treatment .Broadcaster RTHK said later that 24 people had been arrested.
The narrow streets in and around Mong Kok were the scene of some of the most violent clashes during protests in late 2014 to demand greater democracy in the former British colony that returned to Beijing rule in 1997.
Hong Kong Indigenous, a localist group that is fielding acandidate in a Legislative Council by-election in a few weeks,was involved in the protest, the South China Morning Post newspaper reported.
Street tensions appeared to have eased off, but radical protesters and "localists" demanding greater Hong Kong autonomyhave vowed to keep fighting even as China shows signs oftightening its grip.
The clashes in December 2014 came when authorities cleared the last of pro-democracy demonstrators from the streets aftermore than two months of occasionally violent protests that had posed one of the Beijing’s greatest political challenges indecades.//Reuters