Hospitals, morgues and cemeteries across Brazil are being overwhelmed by coronavirus cases as Latin America's largest nation veers closer to becoming one of the world's pandemic hot spots.

Medical officials in Rio de Janeiro and at least four other major cities have warned that their hospital systems are on the verge of collapse, or already too overwhelmed to take any more patients.

Health experts expect the number of infections in the country of 211 million people will be much higher than what has been reported because of insufficient, delayed testing.

Meanwhile, President Jair Bolsonaro has shown no sign of wavering from his insistence that Covid-19 is a relatively minor disease and that broad social-distancing measures are not needed to stop it.

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Key points:

• Brazil has officially reported 53,000 COVID-19 cases and more than 3,600 deaths
• Some Brazilian scientists estimate there could already be more than one million cases
• Rio de Janeiro is erecting several field hospitals to cope with the outbreak, including in the Maracana football stadium

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He has said only Brazilians at high risk should be isolated.

In Manaus, the biggest city in the Amazon, officials said a cemetery has been forced to dig mass graves because there have been so many deaths. Workers have been burying 100 corpses a day — triple the pre-virus average of burials.

So far, the health ministry has confirmed nearly 53,000 COVID-19 cases and more than 3,600 deaths. 

By official counts, the country had its worst day yet on Thursday with about 3,700 new cases and more than 400 deaths, and Friday was nearly as grim.

Experts warned that paltry testing means the true number of infections is likely to be far greater.

Because it can take a long time for tests to be processed, the current numbers actually reflect deaths that happened one or two weeks ago, said Domingos Alves, adjunct professor of social medicine at the University of Sao Paulo, who is involved in the project.

"We are looking at a photo of the past," Mr Alves said in an interview last week.

"The number of cases in Brazil is, therefore, probably even greater than what we are predicting."

Scientists from the University of Sao Paulo, University of Brasilia and other institutions say the true number of people infected with the virus as of this week is probably as much as 587,000 to 1.1 million people.

Health system faces impending disaster

The health ministry said in a report earlier this month that it has the capacity to test 6,700 people per day — a far cry from the roughly 40,000 it will need when the virus peaks.

Meanwhile, health care workers can barely handle the cases they have.

At the mouth of the Amazon, the city of Belem's intensive-care beds are all occupied, according to online media outlet G1. 

As the number of cases rose in the capital of Para state, its health secretary said this week that at least 200 medical staff had been infected. The state is actively seeking to hire more doctors, G1 reported.

What the experts are saying about coronavirus:

The city of Rio de Janeiro plans to open its first field hospital, with 200 beds, half reserved for intensive care.

Another hospital erected beside the historic Maracana football stadium will offer 400 beds starting next month.

Health experts and officials are particularly worried about the virus spreading into the poorest neighbourhoods, or favelas, where people depend on public health care.

Mr Bolsonaro has continued to dismiss health officials' dire predictions about the spread of Covid-19 in the country.

Last week, the president fired a health minister who had supported tough anti-virus measures and replaced him with an advocate for reopening the economy.

Mr Bolsonaro's stance largely echoes that of his counterpart and ally US President Donald Trump, who has been stressing the need to put people back to work as unemployment figures reach Depression-era levels.