Brazilian authorities deployed military aircraft and thousands of soldiers in a bid to tackle the wildfires which have ravaged swathes of the Amazon rainforest.

Porto Velho is the take-off base for the first mission, Defence Minister Fernando Azevedo is reported to have said. Footage filmed near the city on Sunday shows planes taxiing and taking off while images from a day earlier show military vehicles driving along nearby roads.

Two C-130 Hercules aircraft have doused the rainforest with tons of water as authorities scramble to contain the fires which have been burning for three weeks.

An estimated 43,000 soldiers have been made available, officials announced, while security forces have been permitted to tackle illegal deforestation.

World leaders at the G7 summit pledged to help tackle the fires "as fast as possible," French President Emmanuel Macron announced on Sunday.

The deployment comes amid international outcry regarding the escalating fires in the rainforest that produces some 20 percent of the world's oxygen supply.

Brazilian President Jair Bolsonaro, who has previously described rainforest protection as an obstacle to Brazilian economic development, has been heavily criticised for his handling of the situation.