It took guards hours to retake control of the prison 45 kilometers (30 miles) south of Guatemala City, said Rudy Esquivel, a spokesman for the national prison system.
Video broadcast on local media showed worried relatives gathered outside the prison and at the hospital where the injured were taken.
Emergency rescue personnel said most had wounds from firearms or knives.
Guatemala’s prisons are considered powder kegs because of overcrowding and a weak rehab system.
In July of 2016 a riot among prisoners in the town of Pavon in the southeast of the country left 14 people dead.
Guatemala’s prison system has 21 facilities with on-paper room for 6,800 inmates, but they hold nearly 24,000, according to official statistics.