Masked demonstrators threw stones and police fought back with tear gas and water cannons Thursday in Chile as tens of thousands of students hit the streets to protest corruption and education conditions.

The march drew extra momentum from a recent series of corruption scandals battering President Michelle Bachelet's government, adding to the anger of a powerful student movement that has been protesting for years against what activists call one of the world's most expensive and unfair education systems.

"We have to say enough to corruption," said Valentina Saavedra, head of the University of Chile Student Federation, one of the organizations that called the protest.

Carrying posters, waving banners and marching to the beat of drums, students flooded the streets of the capital Santiago and other cities, including Valparaiso and Concepcion.

In Santiago, after a peaceful demonstration that filled several blocks of central avenue Bernardo O'Higgins, masked protesters attacked police with sticks and stones.

Officers used water cannon and tear gas to break them up.

The clashes forced authorities to briefly shut down the avenue.

Police put the number of protesters in Santiago at 40,000. Organizers put it much higher, at 150,000.

Bachelet succeeded in passing the first phase of an ambitious education reform package in November, ending selective admissions policies at public institutions and barring them from making a profit.

But student leaders say she has not gone far enough in overhauling a system inherited from dictator Augusto Pinochet, calling on her to fulfill her promises of free university education for 80 percent of students.

Bachelet's reform agenda has been sidetracked, however, by a scandal involving her son that has caused her popularity to plunge to 30 percent.

Sebastian Davalos, the president's eldest child, is being investigated for influence peddling after revelations emerged that he attended a meeting with a Banco de Chile executive where his wife was granted a $10-million loan that had been rejected by three other banks.

Her company used the money to buy land in central Chile that was then slated to be re-zoned for building construction, enabling the firm to sell it at a $5 million profit.

Two other scandals involving tax fraud and illegal campaign contributions by two of Chile's largest companies, the Penta group and mining firm Soquimich, have also been damaging for the government.