A family of suspected drug traffickers in Mexico lost an arsenal after their 9-year-old boy took a gun to school, leading police to a house full of lethal weapons.

Classmates of the youngster spotted a loaded pistol in his school bag and alerted authorities, a spokesman for police in the northern city of Hermosillo said on Friday.

Police raided the boy's home after confiscating the weapon, which was loaded with bullets known as "cop killers" designed to penetrate bullet-proof vests, he added.

At the house, police found 13,000 rounds of ammunition, various pistols and rifles, including AK-47s, as well as an Uzi submachine gun.

There were also military uniforms, dozens of portable radios and two money counting machines.

An armed man at the house saw the police coming and managed to escape.

A woman inside was arrested. The boy was taken into the care of social workers, the spokesman said.