Brazilians have been plunged into afternoon darkness after the worst rainforest fires in history ravaged the Amazon Forest.

Yesterday, Sao Paulo, the largest city on the American continent, was covered in vast plumes of smoke from massive forest fires which blocked the sun and turned the sky black from 3pm.

Alarmed locals posted photos on social media showing a city that appeared to have plunged into afternoon dusk, comparing it to a coming apocalypse.

Officials with Brazil's National Institute of Meteorology said the dark skies were based on a combination of factors: cold, humid air, and smoke from massive fires burning in the Amazon rainforest several hundred kilometres away.

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"The particulate matter, coming from the smoke produced by these large wildfires that are happening in Bolivia, coupled with the cold, humid air that is off the coast of São Paulo, caused the darkness," Franco Vilela, a meteorologist at Inmet, told Globo.

Environmental activists say the scene was at least partially caused by the often deliberate burning of South American forests to make way for farmland.

Photos released by Nasa show that the rampant wildfires, which have been spreading across the Amazon, can be seen from space.

The photos, captured by Moderate Resolution Imaging Spectroradiometer (MODIS) on Nasa's Aqua satellite, show several fires burning in the states of Rondônia, Amazonas, Pará, and Mato Grosso on August 11 and August 13, 2019.

The Amazon is often referred to as the planet's lungs, producing 20 per cent of the oxygen in the Earth's atmosphere. As the largest rainforest on the planet, it is considered a vital instrument in slowing global warming.

This satellite image provided by NASA shows several fires burning in the Brazilian Amazon forest. Photo / AP
This satellite image provided by NASA shows several fires burning in the Brazilian Amazon forest. Photo / AP

It's also home to about three million species of plants and animals, and one million indigenous people. The fire is being called a "global emergency".

Amazonas, the largest state in Brazil, recently declared a state of emergency over the forest fires, according to Euro News.

As of August 16, 2019, satellite observations indicated that total fire activity in the Amazon basin was slightly below average in comparison to the past 15 years, according to Nasa.

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However, Brazil's official monitoring agency is reporting a sharp increase in wildfires this year.

Brazil's National Institute for Space Research (INPE), a federal agency monitoring deforestation and wildfires, said the country has seen a record number of wildfires this year, counting 74,155 as of Tuesday, an 84 per cent increase compared to the same period last year.

A satellite image shows Amazon bush fires from space. Photo / Nasa
A satellite image shows Amazon bush fires from space. Photo / Nasa

According to the INPE, more than one-and-a-half soccer fields' worth of Amazon rainforest are being destroyed every minute.

The states that have been most affected this year are Mato Grosso, Para and Amazonas — all in the Amazon region — accounting for 41.7 per cent of all fires.

Brazil president Jair Bolsonaro, who once threatened to leave the Paris climate accord, has repeatedly attacked environmental nonprofits, seen as obstacles in his quest to develop the country's full economic potential, including in protected areas.

Bolsonaro and Environment Minister Ricardo Salles are both close to the powerful rural caucus in Congress and have been urging more development and economic opportunities in the Amazon region, which they consider overly protected by current legislation.

Some NGOs, environmentalists and academics have been blaming the administration's pro-development policies for a sharp increase in Amazon deforestation shown in the latest data from the space research institute.

The Government is also facing international pressure to protect the vast rainforest from illegal logging or mining activities.

Citing Brazil's apparent lack of commitment to fighting deforestation, Germany and Norway have decided to withhold more than $60 million in funds earmarked for sustainability projects in Brazil's forests.

Amazonas, the largest state in Brazil, recently declared a state of emergency over the forest fires. Photo / AP
Amazonas, the largest state in Brazil, recently declared a state of emergency over the forest fires. Photo / AP

French and German leaders have also threatened not to ratify a trade deal between the European Union and Mercosur countries to pressure Brazil into complying with its environmental pledges within the Paris Climate Agreement.

Meanwhile, Salles was booed Wednesday as he took the stage at a five-day UN workshop on climate change in the northern state of Bahia — an event he had tried to cancel earlier this year.

Some in the audience shouted while waving signs reading, "Stop Ecocide" or "The Amazon is burning".

Salles spoke briefly, saying climate change needs to be addressed.

The states that have been most affected this year's fires are Mato Grosso, Para and Amazonas - all in the Amazon region - accounting for 41.7 per cent of all fires. Photo / AP
The states that have been most affected this year's fires are Mato Grosso, Para and Amazonas - all in the Amazon region - accounting for 41.7 per cent of all fires. Photo / AP

"People are asking for more and more actions. ... There is an acknowledgement that we are in a situation of crisis and emergency," said Manuel Pulgar Vidal, former environment minister of Peru, who attended the event.

Vidal, who now works for the nonprofit WWF, said the criticism directed at Salles could eventually prod the administration into taking action on climate change.

"There is no room for negationism."

-news.com.au, AP