Students in Chile have resumed their protests for education reforms, with more than 100,000 people taking to the streets of the country.
In the capital, Santiago, riot police fired tear gas and water cannon to break up the march, after being targeted by hooded protesters.
Eight officers were injured and 109 people detained, authorities say.
Students say Chile's education system, traditionally viewed as the best in Latin America, is profoundly unfair.
They say middle-class students have access to some of the best schooling in Latin America, while the poor have to be content with under-funded state schools.
Local media say the massive turn-out in Santiago puts the first big march of the year among the largest in the last two decades.
Students have been campaigning for about two years, but this was the first nationwide protest in 2013.
Police said one of the injured officers is in a serious condition, having been hit by acid.
Authorities calculated around 80,000 protesters on the streets of the capital, but student leaders put the figure as high as 150,000.
Across Chile, the students said as many as 250,000 took part in the protests.
The demonstration in Santiago was largely peaceful, but it came to an abrupt end, following scuffles between hooded protesters and riot police.
Water cannons and tear gas were launched after officers were hit by objects thrown by activists.
Traffic lights and sign posts were vandalised.
Two weeks ago, a smaller protest ended with petrol bombs being thrown at the police, who responded with tear gas and water cannons.
The campaign for educational reform is the biggest protest movement Chile has seen since the return to democracy in 1990.
It started with a wave of mass demonstrations in 2011, which carried on throughout 2012.