"No matter how successful we are, if our Earth dies, we all die," posted one Twitter user.
The virtual anguish over the destruction comes as official figures show nearly 73,000 forest fires were recorded in Brazil in the first eight months of the year - the highest number for any year since 2013.
Most of them were in the Amazon.
That compares with 39,759 in all of 2018, according to the embattled National Institute for Space Research (INPE), which has been in Mr Bolsonaro's cross-hairs since it released data showing a surge in deforestation in recent months.
The head of INPE, the agency tasked with monitoring forest clearing, was sacked over the figures.
While it was not possible on Wednesday to measure the size of the area affected by fires, thick smoke in recent days has reportedly blanketed several cities, including Sao Paulo, and even caused a commercial flight to be diverted.
Forest fires tend to intensify during the dry season, which usually ends in late October or early November, as land is cleared to make way for crops or grazing.
But the WWF has blamed this year's sharp increase in accelerating deforestation in the Amazon, which is seen as crucial to keeping climate change in check.
Mr Bolsonaro hit back on Wednesday, saying "criminal action by those NGOs, to call attention against me, against the Brazilian government" may be the reason for the forest fires.
"This is the war that we are facing," Mr Bolsonaro told reporters.
"The fires were lit in strategic places. All the indications suggest they went there to film and start fires. That's what I feel."
Deforestation under scrutiny
Mr Bolsonaro's comments come as Brazil hosts a UN regional meeting on climate change in the northeastern city of Salvador ahead of December's summit in Chile.
Speaking on the sidelines of the workshop, Environment Minister Ricardo Salles on Wednesday defended the government's efforts to prevent illegal deforestation.
"All the rules on illegal deforestation have been upheld, all strategies have continued to be enforced," Mr Salles said.
"Unfortunately both the states and the federal government suffer because of the economic crisis, budget cuts, which hinders ... enforcement operations."
The forest fires have fueled criticism of Mr Bolsonaro's anti-environment rhetoric, which activists blame for emboldening loggers, miners and farmers in the Amazon.
Norway on Thursday joined Germany in halting Amazon protection subsidies, accusing Brazil of turning its back on the fight against deforestation.
Worsening relations between Brazil and Europe have worried the powerful agriculture sector, which fears a backlash from its key markets.