Protests against bus and underground fare rises in the Brazilian city of Sao Paulo have turned violent.
Police fired rubber-coated bullets and tear gas, and detained more than 200 people. Police say they seized petrol bombs, knives and drugs.
Violence has also been reported at protests in Rio de Janeiro.
Prices for a single ticket in Sao Paulo were raised on 2 June from 3 reals ($1.40, £0.90) to 3.20 reals ($1.50, £0.96).
The authorities say that the rise is well below inflation, which since the last price rise in January 2011 has been at 15.5%, according to official figures.
An estimated 5,000 protesters converged on the streets of Sao Paulo's central area on Thursday - the fourth day of the protests.
The protesters clashed with police, who fired tear gas to try to disperse the crowd.
The demonstrators were mostly university students, but the authorities said there were also groups of anarchists looking for a fight.
Some are reported to have set fire to rubbish in the streets, while others smashed shop windows.
At least 55 people have been injured, according to the Folha de Sao Paulo newspaper. It added that six of its journalists had been wounded, two of them shot in the face.
State Governor Geraldo Alckmin branded the rioters "vandals" and promised to act to avoid a repeat of the violence.
"The police acted with professionalism," Mr Alckmin said, rejecting claims that they had used excessive force.
Brazil's Minister of Justice, Jose Eduardo Cardozo, said the demonstrations were legitimate but resorting to violence and vandalism was unacceptable.
More than 2,000 people also took part in protests against fare increases in Rio, one of the host cities for the Confederations Cup which starts on Saturday.