St. Matthews Mall in Kentucky became the scene of a massive brawl involving 2,000 people, forcing it to shut down and a big police presence to be set up around the perimeter. The chaos was apparently caused by a chain reaction, involving separate fights.

Police first began responding to reports of “disturbances” at 7pm ET on Saturday. But the officers assigned to the mall could not cope with the load.

According to the police, there was “a series of brawls” between people aged 13 to early 20s, which quickly grew to include up to 2,000 people, leaving “the entire mall” affected, NBC reports.

Still A LOT of police at Mall St Matthews after police say up to 2,000 teens were fighting inside and in parking lot pic.twitter.com/R7A9qbOuWL — William Joy (@WilliamWAVE3) December 27, 2015

"As they were responding to those disturbances, others were breaking out. ... Disturbances started to feed on themselves,” police spokesman Dennis McDonald said. "They were just overwhelmed with the number of calls for service and reports of disorder."

The officers had to call for backup, and 50 more officers arrived from five different agencies.

What started as brawls quickly began to interfere with shop closures. By the time it was 8pm, shops had begun to close on police orders. But the brawls became so contagious they quickly turned into a melee: people were hanging onto steel grates, unwilling to let shopkeepers shut their businesses.

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“This was a riot… it was crazy,” McDonald added. "I've been a police officer 33 years, and I haven't ever seen anything like this before… We always plan for worst-case scenario, but this exceeded that.”

Some stores ended up being used as safe havens for those that tried to escape the fighting.

There were also reports of gunshots ringing from inside, but they were not confirmed.

Police maintained a presence until 1am that morning, according to McDonald. "It took about an hour and a half, close to two hours, before things were calm. We’re all tired.”

Businesses in the surrounding area were also recommended to shut.

Surprisingly, for a brawl involving 2,000 people, there were only minor injuries. No arrests were made.

Authorities are still determining the cause of the chain reaction that started it all.

The mess was all but forgotten the following morning, and the mall opened at 11am as normal.