Brazil’s rampant coronavirus outbreak has become a global threat that risks spawning new and even more lethal variants, one of the South American country’s top scientists has warned as it suffered its deadliest day of the pandemic.

Miguel Nicolelis, a Duke University neuroscientist who is tracking the crisis, urged the international community to challenge the Brazilian government over its failure to contain an epidemic that has killed more than a quarter of a million Brazilians – about 10% of the global total.

“The world must vehemently speak out over the risks Brazil is posing to the fight against the pandemic,” said Nicolelis, who has spent most of the last year confined to his flat on the westside of São Paulo.

“What’s the point in sorting the pandemic out in Europe or the United States, if Brazil continues to be a breeding ground for this virus?”

Nicolelis said the problem was not simply Brazil – whose far-right president, Jair Bolsonaro, has repeatedly spurned efforts to combat a disease he calls a “little flu” – being “the worst country in the world in its handling of the pandemic”. “It’s that if you allow the virus to proliferate at the levels it is currently proliferating here, you open the door to the occurrence of new mutations and the appearance of even more lethal variants.”

Already, one particularly worrying variant (P1) has been traced to Manaus, the largest city in the Brazilian Amazon, which suffered a devastating healthcare breakdown in January after a surge in infections. Six cases of that variant have so far been detected in the UK.

“Brazil is an open-air laboratory for the virus to proliferate and eventually create more lethal mutations,” warned Nicolelis. “This is about the world. It’s global.”

The alert came as Brazil hurtled into the most deadly chapter of its year-long Covid crisis, with hospitals around the country collapsing or on the verge of collapse and the average weekly death toll hitting new heights. A record 1,726 fatalities were reported on Tuesday, the highest number since the pandemic began.

“It’s a battlefield,” a doctor in the southern city of Porto Alegre told local television after his hospital’s intensive care unit and mortuary ran out of space.

Nicolelis said Bolsonaro’s failure to halt the outbreak and launch an adequate vaccination campaign had created a domestic tragedy from which Latin America’s most populous nation was unlikely to emerge until late 2022.

“We’ve now gone past 250,000 deaths and my expectation is that if nothing is done we could have lost 500,000 people here in Brazil by next March. It’s a horrifying and tragic prospect but at this point it’s perfectly possible,” he said, predicting a traumatic month as public and private hospitals buckled.

“My forecast is that if the world was appalled by what happened in Bergamo in Italy and what happened in Manaus a few weeks ago, it’s going to be even more shocked by the rest of Brazil if nothing is done.”

Nicolelis claimed Brazil’s crisis now posed an international risk, as well as a domestic one and claimed Bolsonaro – who has sabotaged social distancing, promoted unproven remedies such as hydroxychloroquine and belittled masks – had become “the pandemic’s global public enemy No 1”.

“The policies that he is failing to put into practice jeopardize the fight against the pandemic in the entire planet.”

Bolsonaro, a former army captain who swept to power in 2018 on a wave of anti-establishment rage, has defended his performance, claiming his opposition to Covid restrictions is about protecting Brazil’s economy. “I haven’t gotten a single thing wrong since March last year,” the 65-year-old told supporters this week.

José Gomes Temporão, Brazil’s health minister during the 2009 swine flu pandemic, said Bolsonaro’s response had been so lacking that he and other senior administration figures would eventually “have to be held accountable”.

“To this day, Brazil doesn’t have a national plan to combat Covid-19,” Temporão complained, attacking Bolsonaro’s failure to secure sufficient vaccines by striking deals to buy shots made by companies such as Pfizer, Moderna and Johnson & Johnson. Just 3.3% of Brazil’s population has so far been vaccinated, compared to 15.2% in the US, 18% in Chile and 29.9% in the UK.

“I don’t think there is any other leader who is so obtuse, so backward, who has such a mistaken and warped vision of reality as the president of Brazil,” Temporão said. “History will condemn these people.”