CHINO (CBSLA.com) — Three students were injured Wednesday after an unidentified student pulled the trigger of a police-issued AR-15 rifle during an anti-drugs event at an elementary school in Chino.

The incident took place at 11:40 a.m. at Newman Elementary School, which is located at 4150 Walnut Ave.

The Chino Police Department was giving an anti-drug presentation on the school’s playground when a firearm was accidentally discharged, police said.

CBS2’s Randy Paige spoke to an 11-year-old student who witnessed the incident from a distance.

“The cops were playing with the kids, handball. Four square, I mean,” said Leo Castaneda. “They were giving out stickers.”

While police were not watching a motorcycle with a gun latched to it, Castaneda said a student apparently went over to the rifle and fired it at the ground. The student got startled by the noise and ran into a nearby field, said the witness.

In a Wednesday news conference, Chino officials confirmed that a student was able to gain access to the loaded weapon, described initially as a handgun but later as an AR-15 rifle.

They also pointed out that the rifle was never removed from the motorcycle’s locked mountain device.

Castanada added, “It was crazy. I never thought something like that would happen at school.”

Castaneda’s mother, Anna Mora, was relieved there were no serious injuries but still concerned a student was able to get close to a loaded weapon.

She wants to know why “it was so easy for this student to get [to] the gun?”

In a statement, the city of Chino said, “The Chino Police Department is conducting a thorough investigation into this matter in full cooperation with the Chino Valley Unified School District.”