Hooded protesters hurled Molotov cocktails at a police station in the Chilean capital on Wednesday ahead of a nationwide student demonstration.

Protesters also stoned cars, looted a restaurant to use chairs for barricades and burned tires, blocking rush-hour traffic along some of Santiago's main roads.

"They are not students, they are criminals and extremists," interior and security minister Andres Chadwick told a press conference. "They've acted in a coordinated and planned way to provoke these acts of violence."

Teachers, dock workers and copper miners said they would join students in the national protest to demand education reform.

Chile is the world's top copper producer and its fast-growing economy is seen as fertile ground for investors. But it is also plagued by vast income inequality and a costly education system that many say is unfair.

"This has to do with discontent that is deeply rooted in many sectors of society. But we're the first ones to sympathise with people who are innocent victims of this violence, because there's no way to justify these types of clashes," Andres Fielbaum, president of the University of Chile student federation, told state television.

The march, timed ahead of Sunday's presidential primaries, was aimed at demanding wider distribution of Chile's copper wealth, and reform of the education system that would put the state back in control of the mostly privatised public universities.

Student leaders also want to change the tax system so the rich pay more.

Chilean student protests are often infiltrated by small but violent anarchist groups who throw rocks, firebombs and even acid, while police in riot gear respond with water cannons and tear gas.

Two years of student marches left Chile's major cities regularly paralysed, and stoked expectations of change. The dispute over education reform remains a key electoral issue ahead of the 17 November presidential elections.