A fight between two schoolgirls in a busy park popular with families escalated when one of them pulled a knife on the other.
The girls, aged 13 and 15, are believed to have arranged the confrontation after a falling out on social media.
Video shot by witnesses showed the pair exchanging punches before the younger teenager pulled out the potentially deadly weapon to the shock of the crowd.
Footage shows the pair wrestling with one another before one girl strikes the other in the head repeatedly as witnesses jeer from the sidelines.
They then roll into a nearby hedge and continue to tussle with one another. The girl on top, wearing black, then grabs the other’s arm to stop herself from being hit in the head before the girl on the floor grabs the other’s hair and hits her over the head repeatedly with her free arm.
Suddenly, the girl in black seems to wrestle herself on top of the other and begins pulling her hair before someone in the crows is heard saying: “She’s got a f***ing knife mate, she’s got a f***ing knife.”
The video shows the girl holding the weapon before the crowd called on her to “put it down, now” before the youngster leaves the area.
The older girl’s shocked father said afterwards: “I got a phone call from my daughter at the hospital telling me there’d been a fight in People’s Park between her and another girl.
“Our daughter has wounds to her hand and concussion from the incident, but thankfully she’ll be alright.
“Something isn’t right though if 13-year-old girls are walking around armed with knives. It makes you wonder what sort of environment they’re growing up in.
“There was never anything like that when I was a kid, now some people are scared to let their kids out in general.”
Humberside Police asked for public help as they investigated the incident.
A spokesperson said: “We are appealing for anyone who witnessed an altercation between two young people in People’s Park, Grimsby on the evening of 11th June.
“If you saw the incident and think you may be able to help us with our inquiries, please call our non-emergency number, 101, quoting Log 378 of 11/06/2022.”