'Chain reaction brawl' involving 2,000 people breaks out in US mall

Around 2,000 people – many of them teens – brawled in an outbreak of riotous mass violence in a mall in the US state of Kentucky.

Hundreds of people fought each other and countless numbers ran for their lives as violence exploded in what police described as a "chain reaction brawl" the day after Christmas.

Pockets of violence broke out around 7pm Saturday and spread around the Mall St Matthew, the largest mall in the state, NBC reports.

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Officers on duty at the mall called for back up, with another 50 police arriving as reinforcements.

Police spokesman officer Dennis McDonald said the officers made their around the mall about 8pm to tell stores to close their doors.

"Disturbances started to feed on themselves. They [police] were just overwhelmed with a number of calls for service and reports of disorder," McDonald said.

"This was a riot … It was crazy."

Rioters aged as young as 13 through their 20s fought for close to two hours as police tried to quell the violent mass hysteria.

There were no arrests and only minor injuries were reported.

A town of around 18,000 people, St Matthews sits just outside Louisville but is relatively quiet on the crime front.

Officer McDonald said he has been on the force for 33 year and "I haven't ever seen anything like this before."

"We always plan for worst-case scenario, but this exceeded that."