About 1,500 people have been held in Brazil after supporters of ex-President Jair Bolsonaro stormed Congress, the presidential palace and the Supreme Court in the capital Brasília.
The rioting came a week after President Luiz Inácio Lula da Silva was sworn in.
He condemned the "terrorist acts" and vowed to punish the perpetrators.
Mr Bolsonaro has not admitted defeat in October's tight election that divided the nation, and flew to the US before the handover on 1 January.
On Monday, he was admitted to hospital in Florida with abdominal pain.
Tens of thousands of people are now demonstrating in Brazil's largest city São Paulo in support of democratic values.
The turnout is impressive - a part of Paulista Avenue, Brazil's most famous street, is blocked off - as crowds have filled the area, singing, dancing and chanting for justice, reports the BBC's Katy Watson in São Paulo.
There was however a huge police presence in case of any trouble. At times, the atmosphere has felt tense, our correspondent adds.
The new president - widely known as Lula - and the heads of Congress and the Supreme Court said they "reject the terrorist acts and criminal, coup-mongering vandalism that occurred" during Sunday's riots.
The dramatic scenes saw thousands of protesters clad in yellow Brazil football shirts and flags overrun police and ransack the heart of the Brazilian state.
Lula was forced to declare emergency powers.
On Monday morning, heavily armed officers started dismantling a camp of Mr Bolsonaro's supporters in Brasília - one of a number that have been set up outside army barracks around the country since the presidential election.
Authorities arrested 1,200 people on Monday - in addition to 300 detained a day earlier.
Justice Minister Flavio Dino said some 40 buses which had been used to transport protesters to the capital had been seized.
The scale of the damage was still starkly evident on Monday afternoon, even as officials lauded the progress of the clean-up at the presidential palace, reports the BBC's Bernd Debusmann in Brasília.
He says workers were cleaning up broken glass around the building's exterior. Almost every window on the building's ground floor had been damaged, forcing crews to painstakingly remove each pane of glass and replace it with a new one.
The cobblestone pavement outside the palace also showed signs of damage, with large patches torn out by rioters on Sunday.
"They were using the rocks as missiles," one official said. "To break the glass."
In the nearby Congress building, the damage included valuable works of art, including several high-profile pieces that were reportedly damaged by water or defaced during the riot.
The streets, however, were largely calm and devoid of noticeable military or police presence, our correspondent adds.
Mr Bolsonaro condemned the attack and denied responsibility for encouraging the rioters in a post on Twitter some six hours after violence broke out.
Meanwhile, Brasília Governor Ibaneis Rocha has been removed from his post for 90 days by the Supreme Court.
Justice Minister Alexandre de Moraes accused him of failing to prevent the riot and of being "painfully silent" in the face of the attack. Mr Rocha has apologised for Sunday's events.
Video shared by the Brazilian outlet O Globo showed some officers laughing and taking photos together as demonstrators occupied the congressional campus in the background.
Demonstrators were quick to defend their actions when approached by reporters.
Lima, a 27-year-old production engineer, said: "We need to re-establish order after this fraudulent election."
"I'm here for history, for my daughters," she told AFP news agency.
Others in the capital expressed outrage at the violence and said the attack marked a sad day for the country.
"I voted for Bolsonaro but I don't agree with what they're doing," Daniel Lacerda, 21, told the BBC. "If you don't agree with the president you should just say it and move on, you shouldn't go hold protests and commit all the violence like they're doing."
Bolsonaro supporters created camps in cities across Brazil, some of them outside the military barracks. That is because his most ardent supporters want the military to intervene and make good elections that they say were stolen.
It looked like their movement had been curbed by Lula's inauguration - the camps in Brasília had been dismantled and there was no disruption on the day he was sworn in.
But Sunday's scenes show that those predictions were premature.
Some protesters are not just angry that Bolsonaro lost the election - they want President Lula to return to prison.
He spent 18 months in jail after being found guilty of corruption in 2017. His convictions were later annulled, after initially being sentenced to more than nine years.
Heads of state around the world have also denounced the violence, with the leaders of the US, Canada and Mexico issuing a joint statement on Monday condemning "attacks on Brazil's democracy and on the peaceful transfer of power".
Late on Monday, President Joe Biden "conveyed the unwavering support of the United States for Brazil's democracy" during a phone call with Lula, the White House said in a statement. It added that the Brazilian leader had accepted Mr Biden's invitation to visit Washington in early February.
Comparisons have been drawn with the storming of the US Capitol on 6 January 2021 by supporters of Donald Trump, an ally of Mr Bolsonaro. Mr Biden was sworn in that day after defeating Mr Trump in presidential elections the previous November.