Four inmates died and 16 others were injured in a massive brawl at a prison in the northern Mexican state of Zacatecas, authorities said Friday.

Most of the 490 inmates took part in Thursday's disturbances at Cieneguillas prison, warden Francisco Javier Bernal Ortiz told Radio Formula.

"They hit each other with planks they took from the pews in the church. It was a free-for-all, tough," he said.

The brawl appeared to be part of a struggle for control of the inmate population, the warden said.

All the injuries were caused by planks, poles filed to a point and hunks of stone from benches broken up by the combatants, he said.

The municipal and state law enforcement agencies and the federal police were called in to help the guards restore order, a task that took two hours, according to Bernal.

The Zacatecas state Attorney General's Office has opened an investigation into the incident, the warden said.

Bernal took charge at Cieneguillas prison in the wake of the Aug. 22 disappearance of then-warden Fabiola Quiroz Zarate, who is thought to have been kidnapped.

"There is no knowledge of her whereabouts nor any news in that respect," Bernal said Friday.

Mexico's worst prison violence in five years took place in February at a penitentiary in the northern state of Nuevo Leon, where 44 people were killed to conceal the escape of around 30 inmates from the Los Zetas drug cartel. EFE