The riots began when relatives visited the prisoners, after that about 100 visitors were taken hostage.
At least seven people were reportedly beheaded during the riot while bodies of six more victims are said to have been burned.
Al menos 25 presos han muerto en una pelea entre bandas rivales en una cárcel de la ciudad de Boa Vista. https://t.co/iHoN6XCMTg— Caralangas (@carMoreno45) October 17, 2016
According to Folha de Boa Vista media outlet, the incident was caused by a conflict between members of two warring drug dealer gangs.
Authorities of the Roraima state sent special police units to the prison and managed to release the hostages.