Several buses were set on fire and an electronics store was looted in Sao Paulo late Tuesday following Brazil's crushing World Cup defeat to Germany, police said.
Police did not give a figure but Folha de Sao Paulo newspaper said on its website that some 20 buses were torched in a garage where unused vehicles were stored.
Another three buses were set ablaze in other parts of the mega-city.
Police did not confirm whether the fires were linked to Brazil's 7-1 defeat to Germany in the semi-final, which knocked the national team out of the World Cup it is hosting.
"This is under investigation," a state militarised police spokesman told AFP.
Looters ransacked an electronics store in the east of the city.
Buses are often burned by robbers or as a form of protest in Brazil.
Cry and curse
Brazilians cried, cursed their president and covered their faces in shame after their beloved football team's humiliating 7-1 thrashing by Germany in the World Cup semi-finals Tuesday.
After the fifth goal, well before half-time, hundreds of people left their expensive seats at the stadium in the southeastern city of Belo Horizonte.
A section of the crowd chanted obscenities against the players and President Dilma Rousseff, who during the cup had mostly enjoyed a reprieve from protests over the record $11 billion spent to host the tournament.
The tears began well before the final whistle, with the third German goal in the first half causing children and adults to start bawling in the stadium and in public screenings across the continent-sized nation.
As people streamed out, police reinforced security inside and around the stadium, but no incidents were reported there.
Others around the country shouted at their televisions and abandoned public screenings as the Selecao suffered the biggest defeat of its 100-year history.
"Neymar must be vomiting at home watching this disaster. The horror," said Marina Genova, 54, watching at a popular bar district in Sao Paulo, referring to Brazil's injured star.
Amid the deluge of goals, a downpour only added to the already gloomy mood of thousands of fans in Brazil's canary-yellow jersey at the official "Fan Fest" on Rio de Janeiro's Copacabana beach.
Brazilians were already concerned about the team's chances after Neymar broke a vertebra in the quarter-final victory over Colombia.
But they never thought it would be this bad.
"This is a terrible match and Brazil without Neymar are terrible. I hate this match. It's embarrassing to lose like this," said Beth Araujo, 24, a biology student.
"The only good thing is I think it will affect President Dilma in the election. But all our politicians are even worse than the team," she said.
Rousseff said she was "very sad" and "sorry" about the result.
'Shame of Shames'
Brazil had hoped to exorcise the ghost of its defeat to Uruguay in the 1950 World Cup final in Rio de Janeiro, a national trauma dubbed the "Maracanazo" because it was played in the Maracana Stadium.
This time, TV commentators were talking of the "Mineirazo," after the Mineirao Stadium, with the sports website globoesporte.com calling the defeat the "Shame of Shames."
But Jessica Santos, a 23-year-old photo student, was taking the massacre in stride.
"The cup is back in Brazil for the first time in 64 years so of course we'll cheer until the end," she said. "If Brazil wins, we party, if Brazil loses, we still party. It would have been worse to lose to Argentina in the final."
Others turned to social media jokes to ease the pain, posting pictures of Rio's iconic Christ the Redeemer statue covering its face in shame - or even replaced by German Chancellor Angela Merkel.
It's a disaster
The insults against Rousseff, who is seeking re-election in October, showed that tensions remain following massive demonstrations that rocked the country last year when Brazilians demanded better health care and education.
Some Brazilians have voiced concerns that Brazil's failure to win the World Cup could spark more protests and clashes.
"It's a disaster. It will be chaos. People will break everything. They're going to be furious," said Karina Marques, a 17-year-old footballer who watched the game at a street screening in Rio attended by 30,000 people.
At a squatter camp of homes made of wooden planks outside Brasilia, people turned off their televisions in disgust before the end.
In tears, Maria Jose Costa Almeida, 35, asked: "Why spend so much on stadiums, bring the cup to Brazil, to win nothing?"