An Upper Manhattan high school and neighboring City College were placed on lockdown Thursday morning after reports of someone with a gun in the school, officials said.

Authorities responded to the Philip Randolph Campus High School on West 135th Street near Convent Avenue about 11:40 a.m. following reports of two people with a firearm.

According to law enforcement sources, one student allegedly saw another student showing off a gun.

A male student is in custody and an “imitation pistol” was recovered from the scene, cops said.

Police say the school has been placed on a soft lockdown as a precaution and there does not appear to be any continued danger to students.

The City College of New York, which is adjacent to the high school, was also on precautionary lockdown as a result, school officials said.

No shots were fired and no injuries have been reported, officials said.