CHICAGO (AP) — Police say more than 30 teenagers have been arrested after large groups of high school students caused disruptions and started fights in downtown Chicago.

The Chicago Tribune reports that Chief of Patrol Fred Waller says hundreds of teens were moving through the city Wednesday night and numerous fights broke out. He says teens were arrested for disobeying orders to disperse and trespassing.

Waller says no injuries were reported aside from bruises and bumps.

At one point, teens gathered at Millennium Park, a popular place among tourists. Police moved them out of the park after several fights broke out.

Chicago police have dealt with large crowds of teens swarming downtown before as the weather starts to warm up. Waller says police have “faced this challenge for the past few years coming up with different strategies and trying to do some intervention.”