Chicago Police and the ATF are investigating after a possible explosive device was found on the roof of a school in the Southwest Side Brighton Park neighborhood.

A hole was discovered in the roof of the Columbia Explorers Academy Elementary School at 4520 S. Kedzie Ave. at 9:47 a.m., according to Chicago Police.

As a precaution, the students were taken to an adjacent building during the investigation. No injuries were reported.

The building reopened at 12:10 p.m., police said.

A source said the device was believed to be a firework that went off overnight.