Police chile dam protest
© AP Photo/Luis HidalgoPolice detain another dam protester
Tens of thousands of people massed in the center of Chile's capital Friday night for new protests against the government's plan to dam two wild rivers in the country's southern Patagonia region.

Most demonstrators were peaceful, but bands of hooded protesters attacked police and smashed shop windows and damaged other property along a 10-block stretch of Santiago's main avenue.

The protesters started at the Plaza Italia and walked peacefully to the front of La Moneda presidential palace, carrying flags and banners denouncing the hydroelectric project that was approved for Patagonia on May 9.

At that point, hundreds of masked people began throwing rocks at police, who responded with water cannons and tear gas. The masked bands tore off metal bars and scaffolding timbers to use against police, trashed stores, wrecked signs and set fire to trash piles.

Thousands of other demonstrators sat down on the street and raised their hands in a sign that they were unarmed and not involved in the violence.

The march came a week after another protest against the planned HidroAysen project saw clashes between some demonstrators and police. Authorities had suspended police use of tear gas after that violence, but reinstated its use before Friday's march, citing threats of violence.

Environmentalists and others are angry over the $7 billion plan to build five dams on two free-running rivers in a mostly roadless region of Patagonia known for picturesque Andean glaciers and stunning deep green valleys and fjords.

The government, business groups and economists say Chile needs the dams to generate electricity sorely needed for Chile's booming economy. They say the country should double its electricity production over the next decade.

Critics say more should be done to increase the amount of power obtained from renewable sources, such as solar and geothermal energy.