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.
Uruapan, which is home to a quarter million people, has seen episodes of grisly violence linked to drug cartels in the past.