Chaos broke out overnight in the heart of a busy Hong Kong shopping district during a Lunar New Year celebration as police tried to suppress a protest against authorities’ clampdown on unlicensed street vendors.

During the protest, a traffic cop fired three shots to warn off protesters, but the protests only grew more fierce, with many demonstrators hurling bricks and glass bottles at police. Amid the confusion, more than 90 police officers were injured and 54 people ages 15 to 70 were arrested, according to police. Four journalists were also injured, according to local media.

The protests started around midnight, when food hygiene officials from the semiautonomous Chinese territory began to close in on dozens of street food vendors at a major intersection in the bustling Mong Kok district. When the vendors resisted by pushing their carts to block the roadways, police were called in.

The plight of the hawkers, many of whom sell fish balls and other traditional Hong Kong snacks, has emerged as a symbol of local identity in conflict with a flood of big business and cultural influence from mainland China.

Some Internet users called the demonstration the “Fish Ball Revolution,” a nod to the massive pro-democracy protest movement of 2014 that paralyzed huge swaths of the city. Mong Kok was one of the movement’s biggest protest sites.

About the same time the food vendors were making their stand, a pro-local-autonomy group known as Hong Kong Indigenous was holding a political rally nearby.

About two dozen people from Hong Kong Indigenous wearing royal blue hoodies, some armed with long wooden sticks and carrying homemade shields, rushed to the scene of the food vendor clampdown and appealed to the public to face off with police. A standoff ensued.

About 2 a.m. Tuesday, without warning, a traffic police officer fired two shots into the sky, but no one gave ground. Word began circulating that the food hygiene officials had roughed up some vendors.

Several hundred protesters soon amassed; some tossed water bottles and bricks at police. A pile of cardboard boxes was set ablaze.