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 militarized 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.