A 16-year-old boy was arrested for possession of a loaded gun inside a Manhattan high school Tuesday morning, police said.

The teen was taken into custody at 11:15 a.m. after a school safety officer found a loaded 9-millimeter handgun in his coat pocket at Cascades High School on the Lower East Side, cops and sources said.

Nobody was injured in the incident, police said.

Police are still investigating how the gun was snuck onto school grounds.

Cascades High School does not have a metal detector, a source said.

The incident comes just one day after an 11-year-old girl was taken into custody for trying to sneak a kitchen knife into a middle school in the Bronx. The girl allegedly used the weapon to slash a 12-year-old boy in the arm inside the school.

The boy was immediately taken to Lincoln Hospital where he is in stable condition.

The Department of Education said it plans to provide additional security to the school community in the coming days.

Youth crime has been in focus after a series of high-profile crimes, including a string of robberies involving a moped-riding group of machete-wielding miscreants robbing young people across the city.

All of the suspects are believed to be between the ages of 16 and 18, police said.