Brazilian warplanes are dumping water on the burning forest in the Amazon state of Rondonia after a global outcry over the destruction of the world's largest tropical rainforest, according to a government video.

As of Sunday, President Jair Bolsonaro had authorized military operations in seven states to combat raging fires in the Amazon, responding to requests for assistance from their local governments, a spokesperson for his office said.

About 44,000 troops will be available for "unprecedented" operations to put out the fires, and forces are heading to six Brazilian states that asked for federal help, Defence Minister Fernando Azevedo said. The states are Roraima, Rondonia, Tocantins, Para, Acre and Mato Grosso.

A tract of the Amazon jungle burns as it is cleared by loggers and farmers in Porto Velho, Brazil August 24, 2019. (Ueslei Marcelino/Reuters)

A video posted by the Defence Ministry on Saturday evening showed a military plane pumping thousands of litres of water out of two giant jets as it passed through clouds of smoke close to the forest canopy.

The response comes as leaders of countries in the G7 nations currently meeting in France expressed grave concerns over the fires.

French President Emmanuel Macron on Sunday said the G7 was nearing a deal to provide "technical and financial help" to countries affected by the Amazon fires.

Nearly 80,000 fires have been registered across Brazil through Aug. 24 — the highest number since at least 2013, according to space research agency National Institute for Space Research (INPE).

Bolsonaro announced the military would be sent in on Friday after several days of criticism from the public and world leaders that Brazil's government was not doing anything to fight the fires.

But outside of Rondonia, the government had yet to give operational details for other states. The Defence Ministry said in a briefing on Saturday that 44,000 troops were available in Brazil's northern Amazon region but did not say how many would be used where and what they would do.

The Defence Ministry did not immediately respond to request for more details on Sunday.

Justice Minister Sergio Moro had also authorized a force of military police to assist in fighting the fires, with 30 set to be sent from Brasilia to Porto Velho. The president's office posted to Twitter a photo of police officers on a plane bound for Rondonia set to arrive at noon.

Environment Minister Ricardo Salles posted a video showing a caravan of yellow fire prevention trucks and other government vehicles.

Parabéns Pres <a href="https://twitter.com/jairbolsonaro?ref_src=twsrc%5Etfw">@jairbolsonaro</a> pela adoção de medidas concretas e efetivas. Orgulho servir sob seu comando. <a href="https://t.co/0XuTFnobuZ">pic.twitter.com/0XuTFnobuZ</a> —@rsallesmma

The Amazon is the world's largest tropical rainforest and is seen as vital to the fight against climate change because of the vast amounts of carbon dioxide that it absorbs.

Brazilian climate scientist Carlos Nobre said he worries if 25 per cent of the ecosystem is destroyed that the Amazon could reach a tipping point, after which it would enter a self-sustaining period of dieback as the forest converts to savannah. Nobre warned that it is not far off with already up to 17 per cent of the rainforest having been destroyed.

'We're all worried'

Pope Francis said Sunday that the Amazon forest is vital for our Earth and is urging prayers that fires there are quickly controlled.

Francis added his voice to the chorus of international concern that the blazes in Brazil will have grave repercussions on the world's environmental health.

Pope Francis added his voice Sunday to the chorus of international concern that the blazes in Brazil will have grave repercussions on the world's environmental health. (Gregorio Borgia/The Associated Press)

The pontiff, who is from the South American nation of Argentina that borders Brazil, told the public in St. Peter's Square that "we're all worried" about the vast Amazon fires. He warned that that green "lung of forest is vital for our planet."

Francis said "let us pray so that, with the efforts of all, they are controlled as quickly as possible."

DiCaprio pledges support

A new environmental foundation backed by actor Leonardo DiCaprio is pledging $5 million US in aid to the Amazon, which has been swept by wildfires.

Earth Alliance was created last month by DiCaprio and philanthropists Laurene Powell Jobs and Brian Sheth. On Sunday, it launched the Amazon Forest Fund in an announcement on its website. The alliance is also seeking donations to help repair the Brazilian rainforest, called the "lungs of the planet."

A man holds a Brazilian flag ahead of the demonstration to demand more protection for the Amazon rainforest. (Sergio Moraes/Reuters)

According to the website, 100 per cent of proceeds will go directly to helping protect the rainforest.

The Academy Award-winning actor, known for films like The Revenant and The Great Gatsby, has demonstrated a longtime commitment to fighting climate change. However, he was also called out for spreading inaccurate information when a photo he re-posted on his Instagram last week of the forests burning was found to be from 2018.

Brazilian federal experts reported a record number of wildfires across the country this year, up 84 per cent over the same period in 2018.

The funds will be distributed to five local groups working to combat the problem.