The already vast fortunes of America’s 643 billionaires have soared by an average of 29% since the start of the coronavirus pandemic, which has at the same time laid waste to tens of millions of jobs around the world.

The richest of the superrich have benefited by $845bn , according to a report by a US progressive thinktank, the Institute for Policy Studies.

The report calculated that 643 billionaires in the US had racked up $845bn (£642bn) in collective wealth gains since 18 March, when lockdowns began across the US and much of the rest of the world. The collective wealth of the billionaire class increased from $2.95tn to $3.8tn. That works out to gains of $141bn a month, or $4.7bn a day.

Over the same period, more than 197,000 Americans have died from coronavirus and more than 50m Americans have lost their jobs.

Jeff Bezos, the founder and chief executive of Amazon, who was already the world’s richest person, has benefited most from the pandemic and subsequent global lockdowns. His personal fortune, as estimated by Forbes magazine, has risen by $73.2bn since the start of the crisis to a record $186.2bn. That 65% increase results mostly from the soaring value of Amazon shares as more people turn to the delivery service. In just one day in July, Bezos saw his fortune increase by more than £10bn.

Elon Musk, founder and chief executive of electric car company Tesla, has also benefited from the pandemic. His estimated fortune has risen by 274%, to $92bn, while Facebook’s Mark Zuckerberg has seen his wealth increase by 84% or $45.9bn to $100.6bn.

Bill Gates, who has pledged to give at least half of his fortune to charity and has already pledged a “few billion dollars” to the fight against coronavirus, has seen his estimated fortune grow by 19% to $116bn.

The vast gains have prompted calls for a windfall tax on super-rich tech titans to help pay for the economic recovery from the pandemic.

Senator Bernie Sanders and Minnesota congresswoman Ilhan Omar, both Democrats, have introduced legislation dubbed the “Make Billionaires Pay Act” for a one-off 60% tax on the wealth gains of billionaires between 18 March and the end of the year to help working Americans cover healthcare costs.

Under Sanders’ proposal, Bezos would pay a one-time wealth tax of $42.8bn, and Musk would pay $27.5bn.

Robert Reich, who served as US labour secretary under President Clinton, said “American capitalism is off the rails” and a “wealth tax” was urgently needed to help redress the yawning inequality gap.

“Jeff Bezos could give every Amazon employee $105,000 and still be as rich as he was before the pandemic. If that doesn’t convince you we need a wealth tax, I’m not sure what will.”

“The billionaire economy has been turbocharged by policymakers, who are now stalling on relief for the real economy,” said Chuck Collins, director of the Institute for Policy Studies’ Program on Inequality and co-author of the Billionaire Bonanza 2020 report. “The difference is stark between profits for billionaires and the widespread economic misery in our nation. Clearly, the priorities of elected officials in Washington, DC are completely upside down.”

• This article was amended on 21 September 2020 because an earlier version incorrectly referred to Ilhan Omar as a senator. She is the U.S. Representative for Minnesota’s 5th congressional district.