Supporters of Brazilian far-right ex-President Jair Bolsonaro have stormed Congress in the capital.
The dramatic scenes came a week after left-wing veteran Luiz Inácio Lula da Silva’s inauguration.
Supporters of Mr Bolsonaro – who refuse to accept that he lost the election – broke through barriers and entered the building in Brasília.
Police used tear gas but failed to repel the demonstrators, some of which smashed windows.
It is unclear if they are still in the building.
Footage uploaded to social media also showed rioters storming the nearby presidential palace and the Supreme Court.
Mr Bolsonaro’s supporters are calling for military intervention and the resignation of Mr da Silva – better known as Lula – who defeated his far-right rival in October’s election.
Many are drawing comparisons with the storming of the US Capitol on 6 January 2021 by supporters of Donald Trump, an ally of Mr Bolsonaro.
Lula is currently on an official trip in São Paulo state.
In his inauguration speech, he vowed to rebuild a country in “terrible ruins”.
He decried the policies of his predecessor, who went to the US to avoid the handover ceremony.