New Jersey’s governor, Phil Murphy, said he was “deeply disturbed” by video of a shopping mall brawl that ended with a Black teenager pinned to the ground in handcuffs with a police officer’s knee on his back, while officers let the white youth he had been trading punches with watch from a sofa.

“The appearance of what is racially disparate treatment is deeply, deeply disturbing, and another reminder that progress we’ve made on relationships between law enforcement and the communities they serve … shows that our work is not done,” Murphy said after viewing the video of the weekend altercation at the mall in Bridgewater township.

A Facebook post by the Bridgewater police department acknowledged the incident “has made members of our community upset” and said an internal investigation had been launched.

The Black youth’s mother on Wednesday questioned the responding officers’ handling of the incident while the national association for the advancement of colored people (NAACP) called for the law enforcement pair to be disciplined.

“If it wasn’t for race, then what is it? What made them tackle my son, not the other kid? What made them be so aggressive with my son, not the other kid? Why is the other kid sitting down, looking at my son be humiliated and put into cuffs?” the mother, named only as Ebone to protect her child’s identity, told CNN.

A statement posted to Twitter by the NAACP called on Murphy and the state’s acting attorney general, Matthew Platkin, to remove the two officers from duty.

“Despite years of talk about bias training and accountability … the video cannot be denied. The immediate reaction was to aggressively throw the Black child to the ground, knee placed around the neck area and cuffed behind the back,” it said.

“At the same time, the white youth, at least equally at fault for the fight as his Black counterpart, was carefully eased on to a couch and treated like a victim. This is something that African Americans in New Jersey experience too often.”

National outrage over police treatment of Black individuals built into historic protests following the 2020 murder of George Floyd in Minneapolis when a white officer knelt on his neck for nine minutes. The officer, Derek Chauvin, was convicted of murder while his three colleagues are currently on trial for hate crimes in federal court in St Paul.

The civil rights attorney Ben Crump, who is representing the family of the Black teen in the New Jersey incident, said he was “really troubled”.

“Why is it the Black kid is presumed guilty and the white kid is presumed innocent?” Crump told CNN.

“The Black kid is put face down with a knee in his back and the white kid was allowed to sit on the couch and observe him being humiliated.”

In an interview with local TV station ABC7, the Black youth, whose first name is Kye, said he was defending a younger friend.

“My friend was arguing with the older kid, and so I kind of just jumped into a fight. And since he’s older, he was on top of me and he’s bigger. I was just confused and mad about it,” he said.

“They basically tackled me to the ground, and then the male officer put his knee in my back and started putting me in cuffs. Then the female officer came over and put her knee on my upper back too while [the white youth] was just sitting down on the couch watching the whole thing.”