One minute women were peacefully sunbaking, the next a shocking scene unfolded in front of them.

Another young woman enjoying some sun with her family on the beach was captured being brutally beaten by police.

Emily Weinman can be heard screaming as officers are seen grabbing the 20-year-old around the neck and yanking her by the feet, as onlookers yell "stop screaming" and a baby — understood to be her 18-month-old daughter — is crying in the background.

In the 50-second video that's gone viral around the world, Ms Weinman gets repeatedly punched in the head as police try to restrain her during Memorial Day weekend in New Jersey, news.com.au reports.

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She's later heard screaming, "You're not allowed to hit me like that!" and "I didn't do anything wrong!".

A third cop is also shown keeping other beachgoers away from the violence.

Ms Weinman, who has since been charged over the violent incident as the police conduct gets investigated, said she was at the beach with her daughter, the baby's father and friend and said she had alcohol with her even though she's underage.

She said she was questioned and passed a breath-test but then questioned why police were bothering with them, prompting one cop to respond: "I was gonna let you go but now I'll write you up".

"I had alcohol, it's Memorial Day weekend and 90 per cent of people are underage drinking on the beach, without a doubt,' Ms Weinman wrote.

"It came back negative. I told them I wasn't drinking and the alcohol was clearly closed/sealed, which the cops seen.

"I asked them don't they have something better to do as cops than to stop people for underage drinking on the beach, saying to that there's so much more serious stuff going on."

Ms Weinman said she refused to give the cop her name and was "cautiously" backing away when she tripped and fell and "the cop tackled me to the ground and smashed my head into the sand".

"That's when he head locked me by [putting] his arm around my neck, punched me in my head and then he head locked me again but this time choking me, I was gasping for air," she said.

The shocking scene unfolded in front of dozens of onlookers, many of them families with young children. Photo / Supplied
The shocking scene unfolded in front of dozens of onlookers, many of them families with young children. Photo / Supplied

"Honestly, I can say if I took even a sip, then I would've gave them my information and called it a day; I'm underage, so I know better."

The City of Wildwood Police Department today posted that an Internal Affairs Investigation was immediately launched and the "involved officers have been reassigned to administrative duty pending the outcome of a full and thorough investigation".

Their police chief said while he finds the video to be alarming, he did not want to rush to any judgment until having the final results of the investigation.

Ms Weinman, of Philadelphia, was charged with two counts of aggravated assault on a police officer, aggravated assault by spitting bodily fluids at/on a police officer, disorderly conduct, resisting arrest, obstruction and minor in possession of alcohol.

The video, shared on Twitter by a woman sunbaking on the beach, has been viewed nearly 3 million times.