The fires raging in the Brazilian Amazon are likely to intensify over the coming weeks, a leading environmental expert has warned, despite government claims the situation had been controlled.

About 80,000 blazes have been detected in Brazil this year – more than half in the Amazon region – although on Saturday the far-right president, Jair Bolsonaro, claimed the situation was “returning to normal”.

On Monday Brazil’s defense minister, Fernando Azevedo e Silva, told reporters: “The situation is not straightforward but it’s under control and already cooling down nicely.”

But in an article for Brazil’s O Globo newspaper on Wednesday, one prominent forestry expert warned that the country’s annual burning season had yet to fully play out and called for urgent steps to reduce the potential damage.

“The worst of the fire is still to come,” wrote Tasso Azevedo, a forest engineer and environmentalist who coordinates the deforestation monitoring group MapBiomas.

Azevedo said many of the areas currently being consumed by flames were stretches of Amazon rainforest that had been torn down in the months of April, May and June. But areas deforested in July and August – when government monitoring systems detected a major surge in destruction – had yet to be torched.

The Brazilian Amazon lost 1,114.8 sq km (430 sq miles) – an area equivalent to Hong Kong – in the first 26 days of August, according to preliminary data from the government’s satellite monitoring agency. An area half the size of Philadelphia was reportedly lost in July, with Brazilian media denouncing an “explosion” of devastation in the Amazon.

Azevedo wrote: “What we are experiencing is a genuine crisis which could become a tragedy foretold with much larger fires than the ones we are now seeing if they are not immediately halted.”

He called for urgent measures such as a crackdown on deforestation in indigenous territories and conservation units and outlawing deliberate burning in the Amazon until at least the end of October when the dry season ends.

That warning came after more than 400 members of Brazil’s environmental agency, Ibama, published a damning open letter about the state of environmental protection under Bolsonaro, a rightwing nationalist who took power in January vowing to open up the Amazon to development.

In the letter to Ibama’s president, Eduardo Bim, employees said they felt it was their duty to publicly voice their “immense concern” about the direction environment protection was taking.

“The rates of Amazon forest destruction will not be reduced unless a firm stand is taken against environmental crimes,” they wrote.

Campaigners accuse Bolsonaro’s administration of hamstringing the very agency that should be fighting illegal deforestation and giving the green-light to environmental criminals with his pro-development rhetoric.

On Wednesday Reuters reported that, despite the spike in deforestation, an elite squad of Ibama operatives – called the Grupo Especializado de Fiscalização or Specialized Inspection Group – had not been deployed to the Amazon once in 2019.

At a summit of Amazon governors on Tuesday – supposedly convened to discuss responses to the fires – Bolsonaro repeatedly attacked environmentalists and indigenous activists who he claimed were holding back Brazil’s economy.

Many, though not all, of the Amazon governors backed Bolsonaro’s vision for the region.

“The Amazon is still on fire but Jair Bolsonaro has managed to show he is not alone,” Bernardo Mello Franco wrote in O Globo on Wednesday. “In a meeting at the presidential palace, most of the region’s governors also made it clear they couldn’t give a monkey’s about the forest.”

Bolsonaro confirmed on Wednesday that he would attend a meeting with other South American leaders in neighbouring Colombia on 6 September, in order to draw up a coordinated response to the crisis.

The meeting, announced on Tuesday will seek to draw up a plan to protect the Amazon rainforest, which straddles Brazil, Peru, Colombia, Venezuela, Ecuador, Bolivia, Guyana and Suriname.

On Wednesday 18 global fashion brands including Timberland, Vans and The North Face were reported to have suspended leather purchases from Brazil over the crisis.