Posen Park Fest 2024 was closed due to safety concerns from the altercation, police said.
Police made multiple arrests in connection to the fight, officials said.
Posen's mayor told ABC7 that "civil unrest" broke out around 6 p.m. and the unrest continued for almost two hours.
The carnival was originally supposed to be open until 10 p.m.
"We regret to inform you that due to a large fight at the carnival this evening, we have made the difficult decision to shut it down for the safety of all attendees," Posen police said in a statement to residents.
Residents were asked to avoid the area near the carnival grounds at 147th and Sacramento.
Cell phone video captured large crowds with some people running into the street.
Officer continued to work to clear the area and "disperse the crowd and restore order" after the carnival was shut down.
No further information about the large fight or if there were any injuries was immediately available.