The area around the parliament building in Brasilia had been cordoned off.
Hundreds of supporters of Brazil's far-right ex-president Jair Bolsonaro broke through police barricades and stormed into Congress, the presidential palace and the Supreme Court Sunday, in what President Luiz Inacio Lula da Silva condemned as a "fascist" attack.
Bolsonaro responded to the raids by condemning the "pillaging and invasions" at the National Congress, Presidential palace.
A sea of protesters dressed in the green and yellow of the flag flooded into the seat of power in Brasilia, invading the floor of Congress, trashing the Supreme Court headquarters and climbing the ramp to the Planalto presidential palace.
The shocking images recalled the January 6, 2021 invasion of the US Capitol building by supporters of then-president Donald Trump, a Bolsonaro ally.
Lula, who was in the southeastern city of Araraquara visiting a region hit by severe floods, signed a decree declaring a federal intervention in Brasilia, giving his government special powers to restore law and order in the capital.
"These fascist fanatics have done something never before seen in this country's history," said the veteran leftist, 77, who took office a week ago after beating Bolsonaro in Brazil's bitterly divisive October elections.
"We will find out who these vandals are, and they will be brought down with the full force of the law," he added.
Hardline Bolsonaro supporters have been protesting outside army bases in Brazil calling for a military intervention to stop Lula from taking power since he narrowly defeated Bolsonaro in the October 30 runoff election.
Crowds of protesters scaled to the roof of the iconic Congress building Sunday to unfurl a banner with an appeal to the military: "INTERVENTION."
Social media footage showed rioters breaking doors and windows to enter the Congress building, then streaming inside en masse, trashing lawmakers' offices and using the sloped speaker's dais on the floor of the legislature as a slide as they shouted insults directed at the absent lawmakers.
One video showed a crowd outside pulling a policeman from his horse and beating him to the ground.
Police, who had established a security cordon around Brasilia's Three Powers Square, home to the classic modernist buildings of the National Congress, the Planalto and the Supreme Court, fired tear gas in a bid to disperse the rioters -- initially to no avail.
After failing to repel the invasion, security forces used riot police on horseback and tear-gas bombs fired from helicopters to try to disperse the protesters. But the scenes of chaos continued into the early evening, with huge crowds still gathered at the three buildings.
A journalists' union said at least five reporters were attacked, including an AFP photographer who was beaten by protesters and had his equipment stolen.
'Fraudulent election'
Protester Sarah Lima told AFP they were demanding a review of the "fraudulent election."
Lula narrowly won the runoff by a score of 50.9 percent to 49.1 percent. Bolsonaro, who left for the US state of Florida on the second-to-last day of his term, has alleged he is the victim of a conspiracy against him by Brazil's courts and electoral authorities.
"We need to reestablish order after this fraudulent election," said Lima, a 27-year-old production engineer wearing the yellow jersey of the Brazilian national football team -- a symbol Bolsonaro backers have claimed as their own -- and protesting with her young twin daughters.
"I'm here for history, for my daughters," she said.
Newly-installed Justice and Public Security Minister Flavio Dino called the invasion "an absurd attempt to impose (the protesters') will by force."
"It will not prevail," he wrote on Twitter.
"The (Brasilia) federal district government is sending reinforcements and the forces on the ground are acting at this time."
Senate president Rodrigo Pacheco tweeted he "vehemently rejects this anti-democratic protest, which must be punished with the full force of the law."
There was swift international condemnation of the protesters.
The US said it "condemns any effort" to undermine democracy in Brazil, while National Security Adviser Jake Sullivan said President Joe Biden was "following the situation closely."
European Council President Charles Michel tweeted his "absolute condemnation," French President Emmanuel Macron called for respect of Brazil's institutions and sent Lula "France's unwavering support," as a raft of Latin American leaders joined in.
Chilean President Gabriel Boric called the riots a "cowardly and vile attack on democracy," Colombia's Gustavo Petro tweeted that "Fascism has decided to strike a blow," and Mexican Foreign Minister Marcelo Ebrard voiced the country's "full support" for Lula.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)