The shooting at the "El Rancho" club in the town of Villa Nueva, just outside the city limits, was among the most violent attacks in recent memory in Guatemala.
Three people died at the scene and five others died in hospital, a fire department spokesman told local media.
Police said they found five M16 automatic rifles at the scene, but there was no immediate word on who carried out the attack or a possible motive.
Villa Nueva has been beset by violent crime. Guatemala's rate of 38 murders for every 100,000 inhabitants places it in the ranks of the world's most dangerous countries.