Protesters in the wealthy, industrial city of Santa Cruz brandished placards at the demonstration late on Friday calling for a "punishment vote" against Morales in the upcoming Oct. 20 presidential election.
Tightening polls show Morales, Latin America's longest-serving leftist leader, may be forced into a second-round runoff with his chief rival, Carlos Mesa, a business-friendly former president.
For weeks, opposition candidates and protesters have called on Morales to declare this year's surge in wildfires, which have already scorched an area larger than Costa Rica, a national disaster to help facilitate international aid. Morales' government has said a disaster declaration could invite foreign meddling in a sovereign issue, echoing concerns voiced by neighboring Brazil's far-right President Jair Bolsonaro, who has sparked a global outcry over his handling of fires in the Brazilian Amazon.