Jair Bolsonaro is considering appointing his son Eduardo as ambassador to Washington, the Brazilian leader has revealed, citing the 35-year-old's friendship with the children of US President Donald Trump.

Thousands protested in Brazil on Sunday in support of Justice Minister Sergio Moro, who is battling claims he conspired with prosecutors on his anti-corruption drive to keep former leader Luiz Inacio Lula da Silva from another presidential run.

Tens of thousands of protesters took to the streets in dozens of cities in Brazil on Thursday for a second nationwide demonstration in as many weeks over the government's plan to slash education spending.

At least 40 inmates were killed in four jails in northern Brazil on Monday over an apparent gang dispute, authorities said, in the latest wave of violence to rock the country's severely overpopulated and deadly prison system.

Clashes between inmates killed 15 people at a jail in Amazonas state in northern Brazil on Sunday, the regional prison authority said.

Standing among sacks of used supermarket shopping bags, soft drink bottles and detergent containers, Evelin Marcele is scornful of Brazil's efforts to recycle plastic waste.

Gunmen killed at least 11 people in a bar in northern Brazil on Sunday, officials said.

A Brazilian appeals court on Wednesday ordered former president Michel Temer back to jail, an official said, weeks after the 78-year-old was freed by another judge.  

Brazil's President Jair Bolsonaro on Friday cancelled plans to attend a New York gala in his honor after several companies withdrew their sponsorship and thousands of people demanded it be scrapped.

The gala, organized by the Brazilian-American Chamber of Commerce for May 14, had attracted widespread criticism over the far-right president's record, with New York Mayor Bill de Blasio describing Bolsonaro as "a dangerous man".

A Brazilian appeals court on Tuesday reduced leftist former president Luiz Inacio Lula da Silva's 12-year sentence for bribery and money laundering.

In a unanimous decision, the four judges on the Superior Court of Justice panel hearing Lula's appeal agreed to uphold his conviction, but cut the sentence to eight years and 10 months.