Brazilian authorities have blamed a power struggle between quarrelling Amazon mafiosos for a two-day explosion of prison violence that has left at least 55 prisoners dead.

The slaughter reportedly began at about 11am on Sunday during visiting hours at the Anísio Jobim prison complex in Manaus, the jungle-fringed capital of Amazonas state.

“I was coming out of the pavilion when the massacre started and my son pulled me back inside so I didn’t see,” one elderly woman told the Brazilian broadcaster Globo.

The state governor, Wilson Lima, claimed security forces arrived on the scene within three minutes and had halted the butchery within 45 minutes. By then, however, 15 prisoners lay dead, many reportedly strangled or stabbed with daggers improvised from sharpened toothbrushes - with relatives accusing authorities of failing to stop what they called a massacre foretold.

Relatives of inmates wait for news outside a prison in the state of Amazonas. Photograph: Bruno Kelly/Reuters

“They knew everything that was going to happen – and it happened,” Elcina Lima, the mother of one 24-year-old victim, told A Crítica newspaper in Manaus as she collected his body from the morgue.

On Monday, the bloodshed erupted again and spread to three other nearby penitentiaries leaving another 40 people dead. Most victims were reportedly strangled in their cells using sheets or brute force.

“What we are seeing … is yet another day of terror in the Amazonas prison system,” reported the local journalist Luciano Abreu, recalling how 56 prisoners were killed in the Anísio Jobim complex in January 2017.

That notorious massacre – in which dozens of inmates were decapitated, dismembered and burned – was caused by a turf war between two of Brazil’s most powerful drug factions: São Paulo’s PCC (First Command of the Capital) and the Família do Norte (Northern Family), an Amazon-based group that controls lucrative smuggling routes used to transport Bolivian, Colombian and Peruvian cocaine into Brazil and sometimes on to Europe.

But the regional attorney general, Leda Albuquerque, said the latest slayings appeared to be the result of “a confrontation between the leaders of the same criminal faction”. Reports named those feuding mobsters as the Northern Family’s Zé Roberto da Compensa and João Pinto Carioca.

The bloodbath is one of the first major public security crises for Brazil’s far-right president, Jair Bolsonaro, and Sérgio Moro, the crusading anti-corruption judge who was controversially made head of a newly fused justice and security ministry after helping imprison Bolsonaro’s main election rival, the former president Luiz Inácio Lula da Silva.

Moro ordered members of a federal task force to Manaus on Monday to quell the violence, but commentators from both sides of the political spectrum attacked what they called the sluggish reaction of the security minister, who was reportedly in Portugal attending a seminar.

Conservative pundit Reinaldo Azevedo claimed that on Sunday, “with the corpses already stacked up”, Moro seemed more concerned with tweeting about pro-Bolsonaro demonstrations.

Robert Muggah, the research director at Brazil’s security-focused Igarapé Institute, said the exact cause of the massacre remained unclear, but pointed out that prisons in Brazil were overcrowded and lawless. The country has 700,000 inmates, the world’s third largest prison population after the United States and China.

“We are talking about prisons … in which people are compressed into cells like sardines – often you have 10, 15 or 20 people in cells designed for three, four or five people,” Muggah said.

“It is an understatement to say it is grim; they are medieval conditions in many of these prisons … to the point where a former justice minister famously said he’d rather die than go to a Brazilian jail.”

Muggah said the environment enabled gang violence and organised crime to flourish. “These prisons are out of control and the federal and state governments have manifestly failed to secure them; these are nerve centres of organised crime and they are fiendishly complex problems to deal with,” he said.

Bolsonaro has yet to comment on the killings but has shown little sympathy in the past for the prisoners forced to endure such conditions.

“Do we really have to give these wretches a good life?” Bolsonaro said in 2014. “I’m sorry but they spend their lives fucking us, and those of us who work are expected to give them a nice life in prison? They should just get fucked.”