Prisoners are rioting at a state penitentiary in the Mexican border city of Tijuana.

Red Cross official Fernando Esquer says at least four prisoners are injured with bullet wounds and have been evacuated for treatment.

The riot began Sunday afternoon and quickly escalated. A fire raged on the patio and prisoners have hung messages from the prison's roof and windows. Several messages claim guards have killed at least two prisoners in the past week or so.

Soldiers and police surrounded the building, and a helicopter clattered overhead. Family members trying to find out information on those inside have clashed at least twice with police.

Prison authorities have refused to give any information on the riot.