At least 25 Brazilian prisoners were killed– many of them in the most grisly fashion–after infighting broke out Sunday between rival gangs in a correctional facility in the northern Amazonian city of Boa Vista, shining a spotlight on problems of chronic overcrowding and medieval conditions that plague the country's prison system.

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Of the more than two dozen victims in the violent clashes, seven of the prisoners were decapitated and another six were burned to death, according to the special operations police unit known by the Portuguese acronym, BOPE. The bloody incident took place at the Agricola de Monte Cristo penitentiary in the provincial capital of Boa Vista.

In addition to the deaths, some 100 family members of prisoners — many of them women, in the prison for visiting hours — were taken hostage during the clashes, according to the local Secretariat of Justice and Citizenship. The hostages were released after being held briefly.

The wife of one of the prisoners told the Brazilian newspaper O Globo, that the violent episode erupted when inmates armed with knives and makeshift clubs from one wing broke into another wing of the prison.

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The head of the union of penal workers of the state of Romaira, Joana Moura, told the local newspaper Folha de Boa Vista that the riot reflected the “lack of interest from the state government” to address problems in the prison system. “There is no security equipment, there are not enough personnel for tasks, and the (guards) are working beyond their limits,” Moura said.

The facility is more than 2,000 miles north of Rio de Janeiro, near the border with Venezuela, and is Boa Vista’s largest jail.

Brazil’s incarcerated population doubled in the past decade, ballooning to some 622,000 prisoners at the end of 2014. Harsh sentences for drug-related crimes and a chronically slow judicial system are credited for contributed to the spike in inmate numbers. The majority of prisoners in the country are Black men, according to the Ministry of Justice. Brazil is home to more African-descended people than any country save Nigeria.

Human rights groups have repeatedly raised concerns about the inhumane living conditions in Brazilian correctional facilities, which play an instrumental role in sparking violent clashes.