Brazil's brutal surge in Covid-19 deaths will soon surpass the worst of a record January wave in the United States, scientists forecast, with fatalities climbing for the first time above 4,000 in a day as the outbreak overwhelms hospitals.

Brazil's overall death toll trails only the US outbreak, with nearly 337,000 killed, according to Health Ministry data, compared with more than 555,000 dead in the United States.

But with Brazil's healthcare system at the breaking point, the country could exceed total US deaths, despite having a population two-thirds that of the United States, two experts told Reuters.

“It's a nuclear reactor that has set off a chain reaction and is out of control. It's a biological Fukushima,” said Miguel Nicolelis, a Brazilian doctor and professor at Duke University, who is closely tracking the virus.