Beijing on Monday said it "firmly opposes the violent attack" on government buildings in the Brazilian capital, after hundreds of supporters of ex-president Jair Bolsonaro stormed the country's Congress, the presidential palace and the Supreme Court.

"China closely follows and firmly opposes the violent attack on the federal authority in Brazil on January 8," foreign ministry spokesman Wang Wenbin said.

Beijing, he said, "supports the measures taken by the Brazilian government to calm the situation, restore social order and safeguard national stability".

Far-right Brazilian protesters on Sunday stormed the country's seat of power in riots that triggered an international outcry.

In stunning scenes, backers of Bolsonaro broke through police cordons and overran government buildings in Brasilia, smashing windows and doors and ransacking offices.

Initially overwhelmed security forces used tear gas, stun grenades and water cannon to fight back the rioters until they finally subdued them.

Brazil's recently-elected President Luiz Inacio Lula da Silva has condemned the "fascist" attack and promised those involved will be "brought down with the full force of the law".

"We believe that under the leadership of President Lula, Brazil will maintain national stability and social harmony," Wang told Monday's briefing, describing the South American giant as Beijing's "comprehensive strategic partner". (AFP)