SAO PAULO, Brazil – Police clashed Thursday with students, environmentalists and left-leaning Brazilians protesting a visit by President Bush and his push for an ethanol energy alliance with Latin America’s largest nation.

Riot police fired tear gas at protesters in Sao Paulo after more than 6,000 people held a largely peaceful march, sending hundreds of demonstrators fleeing and ducking into businesses to avoid the gas.

There were no immediate reports of injuries, but some protesters said they had been beaten by officers after marching two miles through the financial heart of South America’s largest city just hours before Bush was scheduled to arrive.

Clashes between police and anti-Bush protesters were also reported in Colombia, where Bush is scheduled to visit on Sunday as part of his five-nation tour to Latin America.

Bush has spoken approvingly of Brazil’s ethanol program, which powers eight out of every 10 new Brazilian cars. The proposed accord is meant to help turn ethanol into an internationally traded commodity and to promote sugarcane-based ethanol production in Central America and the Caribbean.

In Sao Paulo, some carried stalks of sugarcane, used to make ethanol, and a banner reading: “For every liter of ethanol produced, 4 liters of fresh water are consumed, monoculture is destroying the nation’s greatest asset.”

And in the southern city of Porto Alegre, more than 500 people yelled “Get out, imperialist!” as they marched to a Citigroup Inc. bank branch and burned an effigy of Bush.

Fearing that Brazil may clear pristine jungle to increase sugarcane cultivation for ethanol, Greenpeace activists hung a huge banner warning against increased reliance on ethanol as an alternative fuel. They placed the banner on a monument to the 17th century Portuguese explorers who conquered Brazil’s Indians in search of gold and gems.

“We know that Bush and the United States are known for exploiting weaker countries into deals that will only benefit themselves without worrying about the environment,” said Mariana Schwarz, a 25-year-old publicist.

“Bush and the United States go to war to control oil reserves, and now Bush and his pals are trying to control the production of ethanol in Brazil. And that has to be stopped,” said Suzanne Pereira dos Santos, an activist with Brazil’s Landless Workers Movement.

Greenpeace said increased Brazilian ethanol production could cause social unrest.

Associated Press writers Tales Azzoni in Sao Paulo and Mark Stevenson in Mexico City contributed to this report.