Nassau police are investigating how a loaded semi-automatic handgun ended up in the parking lot of Brookside Elementary School in Baldwin, authorities said Tuesday.

There were no reports of injuries after a school security guard found the weapon Monday morning, police said.

A police spokeswoman said school officials called headquarters at 8:50 a.m. Monday to report a gun in the parking lot of the Stanton Avenue school.

The security guard on routine patrol found the weapon and police responded to the scene to recover it, according to a Nassau police news release Tuesday afternoon.

“It was a handgun and it was loaded and in the parking lot,” the spokeswoman said.

No other information about the discovery of the gun, including its exact location in the parking lot, was available from police, the spokeswoman said.

advertisement | advertise on newsday

“It’s an active investigation,” she said.

Robert Leonard, a spokesman for the Baldwin school district, said a security guard put out cones to guide traffic as the school day began Monday and nothing out of the ordinary was discovered while that was taking place. Later in the morning, when the guard went to retrieve the cones, he found the gun “in the proximity of the cones,” Leonard said.

A woman who answered the phone in the school’s main office Tuesday morning who asked not to be identified said, “We aren’t able to discuss an ongoing investigation, but our students and staff were never endangered.”

Detectives ask anyone with information regarding the incident to contact Nassau County Crime Stoppers at 800-244-8477. All callers will remain anonymous.