Fires in Brazil's Amazon rainforest rose by almost 20% in June - a 13-year high for the month, according to government data.
With such an increase at the start of the dry season, there are concerns that this year's fires could surpass 2019's disastrous blazes.
Activists say the coronavirus pandemic is exacerbating the problem.
They believe arson is likely to be even less monitored while authorities are stretched.
Many forest fires in the country are started deliberately by illegal loggers and farmers wanting to quickly clear ground.
Brazil has the world's second-highest coronavirus death toll, after the US, and there are also concerns that increased smoke could have a damaging effect on the breathing of virus patients.
In June, the country's National Institute for Space Research (INPE) recorded 2,248 fires using satellite imagery, as opposed to 1,880 fires in June 2019.
The burning usually increases throughout July, August and September.
"We cannot allow the 2019 situation to repeat itself," Mauricio Voivodic, executive director of the World Wildlife Fund NGO in Brazil, told the Folha de Sao Paulo newspaper, accusing the government of inaction.
Last year's fires peaked in August, with 30,901 - threefold the number for the same period the previous year.
The 2019 fires led to protests domestically and internationally, with threats of financial penalties from foreign governments, and broad condemnation of President Jair Bolsonaro's environmental policies.
The president has been criticised for slashing the Ministry of the Environment's funding, and encouraging business over conservation.
BBC analysis in 2019 showed that a sharp drop in fines for environmental violations during his administration had coincided with the increase in fires.
However, the president has consistently rejected criticism from abroad. "Certain countries, instead of helping ... behaved in a disrespectful manner and with a colonialist spirit," he said in September, rejecting the "misconception" that the Amazon is the lungs of the world.
The Amazon - which spans multiple South American countries but is 60% in Brazil - is a vital carbon store that slows down the pace of global warming.
It is home to about three million species of plants and animals, as well as some one million indigenous people.
Last year, the BBC reported how an area of Amazon rainforest roughly the size of a football pitch is now being lost every single minute, according to satellite data.
Scientists say it could be close to "the tipping point", when its nature completely changes.
This will happen when total deforestation reaches between 20% and 25% - which could be in the next 20 or 30 years.