Image copyright Jeff Nascimento Image caption Darkness descends on Sao Paulo at 16:00 (20:00 GMT) due to smoke from forest fires

A daytime blackout in a Brazilian city has prompted millions of people to voice their concerns for the welfare of the Amazon rainforest.

Sao Paulo was blackened for around an hour on Monday after strong winds and a cold front brought in smoke from forest fires burning in the states of Amazonas and Rondonia, more than 2,700km (1,700 miles) away.

Sao Paulo resident Gianvitor Dias told the BBC what it was like in the city during the smoke-filled blackout on Monday afternoon.

"It was as if the day had turned into night," he said. "Everyone here commented, because even on rainy days it doesn't usually get that dark. It was very impressive."

The hashtag #PrayForAmazonia started to be widely used on Tuesday as a result and there have been more than three million tweets since.

Pictures not all that they seem

People have taken to social media to criticise reports of a massive yearly increase in forest fires. But some of the most striking - and viral - pictures shared by social media users are not all they seem.

The most widely shared tweet using the #PrayForAmazonia tag - with more than a million likes and retweets - includes two aerial images of forest fires, neither of which show the current situation.

One dates as far back as 1989. And other widely shared images include fires as far away as Siberia or the United States.

Even French President Emmanuel Macron shared one of these images.

A video of a Pataxo woman angrily accusing illegal ranchers of starting fires has almost five million views. But the video has been shared on social media since at least July. So while it may point to one potential reason for the reported increase in forest fires, it's not necessarily a depiction of the present situation.

Some of the most popular tweets online are also criticising President Jair Bolsonaro for not taking action.

Scientists from Brazil's National Space Research Institute (INPE) say the Amazon has suffered losses at an accelerated rate since Mr Bolsonaro took office in January.

But the president responded by saying the data "doesn't relate to the reality" and accused them of smearing the country's reputation abroad.

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Image copyright Reuters Image caption President Bolsonaro has contested the institute's data as lies

The president's denial of the data which the Institute says is 95% accurate, is something that is being picked up by social media users.

In a tweet that's been liked more than 10,000 times Twitter user Bea commented that Jair Bolsonaro does not care about the Amazon rainforest. She goes on to express concern at the lack of media coverage towards the fires. She says "people are not talking about it... our greatest natural heritage is being destroyed! We need to wake up and see the reality!"

Other people are voicing their concern about damage the fires are doing to the environment and to nature in one of the world's most iconic ecological areas.

In a post that's been liked 17,000 times, Twitter user William Barros highlighted how the world had celebrated Brazil's natural environment at the opening ceremony of the Rio Olympic Games, only to see it burning to the ground today.

He said: "Three years ago the world saw Brazil celebrating nature and encouraging environmental preservation at the opening of the largest sporting event on the planet.

"Today we see the Amazon, our greatest wealth, on fire for over 16 days. Setback? #PrayforAmazonia."

Other prominent hashtags being used include #prayfortheamazon, #prayforamazonas and #amazonrainforest.

The state of Amazonas declared a national emergency earlier this month because of the forest fires, the fourth most affected area in Brazil this summer.

NASA satellite images show the extent of smoke coverage across swathes of Brazil, Bolivia and Paraguay.

The fires have come at a time when concerns are being raised over the levels of deforestation taking place in the Amazon.

This article was first published on Tuesday 20 August and has since been updated.