Wildfires, mostly started intentionally, have scorched almost 600,000 hectares of land in eastern Bolivia already this year, authorities said.
On Monday night there were 20 active fires in Santa Cruz state affecting seven protected areas.
The government said 200,000 hectares (495,000 acres) had burned in just two days.
Most of the fires are in the forests of Chiquitania, a region that lies between the Amazon to the north, the plains of Cahco to the south and the Pantanal – the world's largest wetland – to the southeast.
The San Matías nature reserve – a national park the size of Belgium – is one of the worst affected areas.
Volunteer firefighters and forest rangers have been digging trenches to try to halt the spreading fires.
The government has deployed around 1,800 military personnel to help, with two helicopters due to join in the effort.
Despite a lack of resources to fight wildfires, Bolivia cannot ask neighboring countries for help unless local and regional authorities declare a "disaster," said Juan Carlos Calvimontes, the deputy civil defence minister.
A disaster can only be declared once the government exhausts its budget for fighting wildfires.
This law "needs to be changed," said Calvimontes.
The government says most of the fires were started deliberately.
Environmentalists blame laws enacted under former leftist president Evo Morales, who for years encouraged burning of forest and pasture land to expand agricultural production.
The practice is legal in Bolivia for areas up to 20 hectares between May and July – once the rainy season is over.
Penalties for illegal fires can be remarkably lenient, though, amounting to a fine of just one US dollar per hectare burnt.
However, for large scale wildfires, perpetrators can be given a sentence of up to three years in prison.