A 14-year-old boy carrying a loaded ghost gun ran from San Mateo police at Los Prados Park and was arrested after a brief foot chase, the department said.

Officers patrolling the park around 10:07 p.m. Tuesday, Oct. 13, found six people near the Casa de Campo parking lot after the park had closed, according to an Oct. 15 department press release. The park closes at 10 p.m. The teen, who was wearing a full face covering, grabbed his waistband and ran south toward Casa de Campo, police said.

He stopped and surrendered after about 50 yards.

During the pursuit, officers noticed the teen repeatedly reaching toward his waistband. Police said they determined he was trying to secure a firearm that had been slipping down his pants as he ran. A search found a loaded 9mm handgun with no serial number concealed in his waistband, according to police.

Privately made firearms produced without a manufacturer’s serial number are commonly called “ghost guns” because they can be difficult to trace, according to the Bureau of Alcohol, Tobacco, Firearms and Explosives.

The teen, a San Mateo resident, was booked into Hillcrest Juvenile Hall on suspicion of offenses including carrying a concealed firearm, minor in possession of a handgun, possession of live ammunition by a minor, possession of an unserialized firearm and resisting a peace officer, according to police.

Earlier juvenile firearm arrest

The arrest came 11 days after San Mateo police seized another unserialized firearm from a juvenile. On Oct. 2, officers stopped a vehicle near East Fourth Avenue and Railroad Avenue for a lighting equipment violation, according to a separate SMPD press release. The driver, a 17-year-old San Mateo resident, was the sole occupant.

Officers reported smelling marijuana and found an open container of it inside the vehicle. A search turned up a loaded, unserialized Glock-style pistol and more than an ounce of marijuana, police said. The 17-year-old was booked into Hillcrest Juvenile Hall on suspicion of offenses including carrying a loaded firearm in a vehicle and minor in possession of a handgun, according to police.

Residents can request nonemergency police assistance at 650-522-7700.