Riot police in the Chilean capital, Santiago, used tear gas and water cannons to disperse hundreds of young people holding an annual protest.
The clashes came as demonstrators marked the anniversary of the 1985 killing of two students by police.
About 500 people were arrested for throwing rocks and Molotov cocktails, the authorities said.
Tension was higher this year amid public anger over chaos caused by Santiago's new transport system.
Hundreds of young demonstrators, many of them high school students, gathered in central Santiago to commemorate what they call "The Day of the Young Combatant".
The protest is organised by far-left groups to honour two students killed by police in 1985 during a demonstration against the military government of General Augusto Pinochet.
The authorities said this year's arrests were higher than those registered during previous protests.
The annual protest is often marked by violence, but this year it came amid continuing anger in the capital over the new public system introduced in February.
The Transantiago system came under further strain with the start of the school year in March, leaving large areas of the capital without public transportation.
President Michelle Bachelet, who has seen support for her government fall, sacked four ministers earlier this week and apologised for the chaos Santiago residents have had to endure.
Some 4,000 police officers were deployed around the city ahead of Thursday's demonstrations.
The protests were, however, far smaller than huge demonstrations last May, when hundreds of thousands of students took to the streets of the capital to call for education reform and lower transport fares. .