(CNN) At least nine people -- four of them minors -- have been killed and two others wounded in a shooting at a video arcade in Mexico.

The massacre happened in Uruapan, in the western Mexican state of Michoacan, on Monday, according to the state's attorney general's office.

Four people walked into the amusement arcade, asked questions of some patrons and began firing with military-grade weapons, the attorney general's office said in a statement.

At least four of the dead are minors between the ages of 12 and 17, the statement added. An 18-year-old and a 39-year-old are also among the dead.

Authorities said they had located 65 "ballistic elements" that matched a 9mm caliber weapon.