Nine inmates were killed and two of them were left decapitated when a riot broke out at a prison facility in the central state of Goias in Brazil. But, the cause of the riot remains unknown.

Authorities say one of the gangs launched an attack on a rival clan and burnt their mattresses late on Monday, 1 January, prompting the second group to retaliate. This led to a riot-like situation at the Colonia Agroindustrial prison, bringing down at least two sections of the jail.

While bodies of the most deceased inmates were found charred, two bodies were found with severed heads. Firefighters managed to douse the fire after hours of struggle. Officials are yet to identify the victims since most require DNA examination, but have confirmed the death toll.

At the time of the jailbreak on New Year's Day, there were about five officers on duty guarding nearly 900 inmates.

"It was an unfortunate situation, many cruel deaths. Many bodies were charred, two had their heads severed and some of them had their viscera exposed. The outlaws, in reality, the majority were of the wings that were attacked. I believe that many were fleeing from the very attack. It was a very serious situation. Two wings were practically destroyed," senior official Semiaberto de Aparecida de Goiânia told the Brazilian news site G1.

Gunfire also erupted during the unrest and nearly 100 inmates have managed to escape. Police had later recaptured up to 30 inmates while rest of them are still at large. Few others have also turned themselves into security officials voluntarily.

Military personnel were also called in during the two-hour-long operation to control the situation. Family members of the inmates have gathered outside the facility to look for their relatives. "My brother is inside and I don't have any information about him. No-one tells us anything. No-one tells us who is dead, who is alive, who was shot," a victim's sister Luana Cristina told O Popular newspaper.

The latest episode has yet again underscored Brazil's severely overcrowded and understaffed prison facilities, where officials are struggling to impose the infamous violent penal system. It also sends a grim reminder of a prison riot, which took place exactly a year ago, during which as many as 56 people were killed. Similar prison riots are frequently reported as the inmates often get access to drugs and weapons while criminal factions controlling the facilities.

Brazil prison riot
An inmate takes a selfie on the roof during an uprising at Alcacuz prison in Natal, Rio Grande do Norte state, Brazil Nacho Doce/Reuters file photo