Three inmates were decapitated and one was asphyxiated in the Desembargador Raimundo Vidal Pessoa jail in Manaus city, CNN reported citing the Amazonas State Penitentiary Administration Secretariat.
Video footage in local media showed heavily armed police officers entering the prison.
The jail, which was shut down in October because of improper conditions, was reopened last week after deadly uprisings at other prisons in Brazil. Nearly 300 prisoners had been transferred to the jail, with state authorities saying they would remain for three months.
On January 1, at least 56 prisoners died in a riot at the Anisio Jobim Penitentiary Complex, also in Manaus.
A Friday riot at the Agricultural Penitentiary of Monte Cristo, in Brazil’s Roraima state in the Amazon, left at least 33 people dead, authorities said.
Brazil has the fourth largest prison population in the world, with more than 622,000 people behind bars, according to its justice ministry.