BRAZIL: Riot police fired tear gas at protesters and beat them with batons just before President Bush began a five-nation Latin America tour.

Students also lobbed rocks and home-made explosives at police on a university campus in the Colombian capital of Bogota, where Bush is due to visit on Sunday.

The violence in Sao Paulo happened several hours before Bush arrived.

More than 6000 people held a largely peaceful march through the financial heart of Brazil.

Protesters said scuffles broke out when some radical demonstrators provoked officers and threw sticks.

After the clash, the protest continued peacefully, but with far fewer people.

They condemned Bush, the war in Iraq and plans to set up an alliance between Brazil and the US over the production of ethanol to power cars.