Many of the victims were beheaded, disemboweled or dismembered, officials said.The state government said the situation was now "under control."
New Grisly Brazil Prison Massacre Kills 31
Brazil was hit Friday by its second grisly prison massacre in a week, as inmates beheaded and mutilated fellow prisoners at a northern jail, leaving 31 dead.
Pictures taken by a police officer at the scene showed bloodied, mangled bodies piled in a concrete hallway at the Monte Cristo Farm Penitentiary (PAMC) in Roraima state.
Many of the victims were beheaded, disemboweled or dismembered, officials said.
The state government said the situation was now "under control."
They lowered an earlier death toll of 33 to 31 late Friday.
"No shots were fired. The victims were killed with sharp objects and home-made weapons," said state justice secretary Uziel Castro.
The latest unrest came days after jailed gang members killed 56 rivals in a 17-hour bloodbath Sunday and Monday at a prison in Manaus, the capital of the neighboring state of Amazonas.
Unlike that incident, Friday's violence did not appear to be an all-out riot but rather a rapid, early morning attack by one group of inmates against another, lasting less than an hour, a local government spokeswoman told AFP.
Most of the killings were carried out with knives, she said.
Deadly prison riots have intensified in Brazil since a truce broke down in July between the country's two largest drug gangs, the First Capital Command (PCC) and the Red Command (CV).
PAMC, the largest prison in the state, was also hit by deadly violence in October, when fighting between rival gangs killed 10 inmates.
At the time, the prison held 1,400 inmates -- double its capacity.