Part of a World Cup stadium in Sao Paulo has collapsed, causing "significant damage," the Associated Press reported.
Television images showed a large metal structure had buckled, destroying part of the stand on the east side of the Itaquerao stadium in Brazil.
Protests took place in dozens of Brazilian cities on Saturday over government corruption, the poor quality of public services, the hosting of the current Conferations Cup and next year's 2014 FIFA World Cup in Brazil.
Police in the Brazilian city of Sao Paulo struggled to prevent protesters from entering city hall during mass protests last night.
Footage from local TV stations showed demonstrators smashing the windows of the building with guard rails.
Earlier in the day, tens of thousands of protesters held a largely peaceful rally outside Sao Paulo Cathedral where a puppet of the city's mayor was burned.