Story highlights Police: Melee started when crowds tried to forcefully enter the R&B and hip-hop concert

But witnesses offered a different account

(CNN) A hip-hop and R&B concert in New Jersey erupted into chaos Sunday night when police in riot gear tried to contain agitated crowds.

The melee started when attendees tried to forcefully enter the Summer Jam concert at MetLife Stadium in East Rutherford, authorities said.

"Security personnel at one of the entrance gates ... were confronted by crowds attempting to illegally enter the sold out Summer Jam concert by climbing over fences and forcing their way through security personnel," New Jersey State Police said.

Troopers on site asked for extra backup to help maintain order, Sgt. Gregory Williams said. Witnesses said authorities arrived in riot gear.

"We have the riot gear all the time and we were ready in case something was to happen and we had to use it," he said.

Armored vehicle with LRAD now blocking the entrance to MetLife Stadium. #SummerJam pic.twitter.com/rpU2QRBMca — The FADER (@thefader) June 8, 2015

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