The fire has already burned more than 3,200 square kilometres of pastures and forests in the central Brazilian region of Mato Grosso.

Fires fuelled by worst drought in 30 years

Brazilian environmentalists declared a "red alert" as the flames were spotted about 4km from Xingu National Park.

The park is home to more than 5,000 members of 17 indigenous Indian groups.

Brazil's Environment Institute has put a new rapid response plan into action for the first time, sending 30 firemen on an air force plane to the burning area.

The plan was drawn up earlier this year after huge fires raged out of control through savanna and rain forest on the northern border.

BBC correspondent Lucio Mesquita: ''Little time left to act''.

During the dry season, slash and burn practices in rural areas are responsible for tens of thousands of fires throughout the country.

But this year has seen a 69% increase in fires during the traditional slash and burn months from June to August, according to the Brazilian newspaper, Jornal da Tarde.

State of emergency

The Brazilian government has released nearly $13m for a new programme to prevent, detect and fight fires across the country.

Indian tribes and the armed forces have been called on to help tackle the Mato Grosso blaze.

Yanomami Indians tackle fire in March

But environment officials say a lack of infrastructure in the region is hampering their work. The nearest town has only one police car and no firefighting equipment.

Regional authorities have declared a state of emergency and conscripted all vehicles to help firefighting efforts.

A change of wind speed slowed down the fire's approach to Xingu National Park, reducing the immediate risk to the 2,000,000 hectare Indian reserve.

A spokesman for the government's National Indian Foundation said: "The fire could be in the park very quickly.

''The situation is very serious. We have declared red alert."

Xingu National Park is considered the showpiece of Brazil's efforts to protect the country's Indian peoples from the modern world.