Police are searching for a suspect who allegedly brought a gun into a Philadelphia high school this morning, prompting a lockdown.

The incident happened around 10:30 a.m. at Kensington Urban High School, on East Cumberland Street near Coral, officials said. According to school district spokesman Fernando Gallard, a student reported an unknown person flashing a gun at him on the first floor before exiting the school. The school was briefly placed on lockdown, but that has been lifted.

Gallard said police have not confirmed that a gun was involved. He said footage from a surveillance camera shows the unidentified suspect entered the school through a side door that was held open by students who were exiting the building.

The incident remains under investigation.