A 13-year-old boy was arrested Tuesday after he took a loaded handgun to a middle school in Prince George’s County, Md., according to police and a school district spokeswoman.

       The incident occurred at Isaac J. Gourdine Middle School in Fort Washington, where officers responded to a report of a student with a gun about 8:15 a.m., police said. They said officers found the student in a classroom and took him into custody without incident after finding the weapon in his waistband. No one was injured.

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       The school was on lockdown for about 90 minutes starting at 8:15 a.m., schools spokeswoman Meghan Gebreselassie said. Authorities did not identify the boy because he is a juvenile. They said charges against him were pending.

       Some students saw the student with the gun and alerted school staff members, Gebreselassie said.

       The firearm was a “ghost gun” without a serial number, police said. Such weapons are often assembled from kits or are 3D-printed from instructions purchased on the internet or at gun shows. The origins of such guns are typically difficult or impossible to trace.

       Nicole Asbury contributed to this report.