Brazilian President Jair Bolsonaro has said his government lacks the resources to fight a record number of wildfires burning in the Amazon rainforest, just weeks after telling donors he did not need their money.

"The Amazon is bigger than Europe, how will you fight criminal fires in such an area?" he asked reporters as he left the presidential residence.

"We do not have the resources for that."

Government figures show, fires in the Amazon have surged 83% so far this year compared with the same period a year earlier, , destroying vast swathes of a forest considered a vital bulwark against climate change.

Although fires are a regular and natural occurrence during the regular dry season at this time of year, environmentalists blamed the sharp rise on farmers setting the forest alight to clear land for pasture.

French President Emmanuel Macron said on his twitter account the fires in the Amazon forest are an international emergency and should be discussed by the G7 summit that will begin on Saturday in Biarritz, France.

Federal prosecutors in Brazil have said they are investigating a spike in deforestation and wildfires raging in the Amazon state of Pará to determine whether there has been reduced monitoring and enforcement of environmental protections there.

Prosecutors also said they will investigate an ad reportedly published by a local newspaper last week encouraging farmers to participate in a "Fire Day," in which they would burn large areas of forest "to show Bolsonaro their willingness to work."

The probe is being led by prosecutors in the cities of Santarém, Itaituba, Altamira and Belém.

Yesterday, Mr Bolsonaro said, without supporting evidence, that non-governmental organisations were behind the fires.

Questioned again today about those comments, he said he could not prove that NGOs, for whom he has cut funding, were lighting the fires but that they were "the most likely suspects."

The right-wing president has repeatedly said he believes Brazil should open the Amazon up to business interests, to allow mining and logging companies to exploit its natural resources.

"As NGOs lose funding ... What can they do?" he asked.

"Try to take me down, try to take me down. That's all that's left for them to do."

Brazil is facing growing international criticism over its handling of the Amazon, 60% of which lies in the country.

Earlier this month, Norway and Germany suspended funding for projects to curb deforestation in Brazil after becoming alarmed by changes to the way projects were selected under Mr Bolsonaro.

At the time, when asked about the loss of German funding, Mr Bolsonaro said: "Brazil does not need that."

Other officials have expressed concern over the fires.

Rodrigo Maia, Brazil's lower house speaker, said on Twitter he would create "an external committee" to monitor the burning of the rainforest. He also vowed to form a group "to evaluate the situation and propose solutions to the government."

The Bishops Conference for Latin America expressed concern about what it called "a tragedy," and called on countries to take immediate action to protect the rainforest and the communities that live in and around it.

"We urge the governments of the Amazon countries, especially Brazil and Bolivia, the United Nations and the international community to take serious measures to save the world's lungs," the Bishops Conference said.

"If the Amazon suffers, the world suffers," the statement said.