The right-wing populist told a group of television reporters that he had developed symptoms at the weekend.

"It started on Sunday with a certain malaise and became worse throughout the day on Monday, feeling poorly, exhaustion, a bit of muscle ache, fever hit 38 [degrees Celsius]," he said.

Finishing the interview, he stepped back and removed his mask to reveal a smile, adding: "You can see from my face that I'm well and I'm calm."

Bolsonaro said he has been taking hydroxychloroquine, an anti-malarial drug with unproven effectiveness against COVID-19.

Bolsonaro has emulated his political role model Donald Trump in voicing skepticism about the virulence of the virus, although the US president has moderated his tone. Bolsonaro tested negative in March for the coronavirus after several aides were diagnosed following a visit to Trump's Mar-a-Lago, Florida, resort.

The positive test on Tuesday looks set to spark a frantic period of contact tracing and tests for those who met Bolsonaro in recent days, including Economy Minister Paulo Guedes, lender Banco Bradesco's Chairman Luiz Carlos Trabuco and planemaker Embraer's CEO Francisco Gomes Neto.

Over the weekend, Bolsonaro was also in close contact with US Ambassador Todd Chapman during July 4 celebrations. Pictures showed neither wearing a mask.

Brazilian financial markets retreated following the news. Brazil's currency, the real, swung into negative territory and the benchmark stock index deepened losses to 1.5%.

Criticism

Brazil has the world's second-largest outbreak behind the United States, with more than 1.6 million confirmed cases.

Bolsonaro has drawn criticism from public health experts for fighting state and city efforts to impose social distancing, arguing that the economic damage of those orders is worse than the disease itself.

He has fired two health ministers during the crisis, both trained doctors, and replaced them with an active duty army general on an interim basis.

He joins a list of government leaders to become infected with the coronavirus, including British Prime Minister Boris Johnson and Honduran President Juan Orlando Hernandez, both of whom were treated in hospital and needed extra oxygen.

Pan American Health Organization director for communicable diseases Marcos Espinal wished Bolsonaro a "speedy recovery" but said his infection carried a message.

"The message is that this virus is unpredictable and does not respect race, class or people in power, despite security around any president," Espinal said. "For Brazil, the infection of its president should reinforce the need to strengthen implementations of social distancing recommendations and the use of masks to mitigate the spread of coronavirus," he added.

Bolsonaro has often defied local guidelines to wear a mask in public, even after a judge ordered him to do so in late June. Bolsonaro has also railed against social distancing rules supported by the World Health Organization.

The US embassy in Brasilia said via Twitter on Monday that the ambassador had lunch on July 4 with Bolsonaro, five ministers and the president's son, Congressman Eduardo Bolsonaro. The ambassador had no symptoms, but would undergo testing and is "taking precautions," the embassy said.