The three richest people in the US – Bill Gates, Jeff Bezos and Warren Buffett – own as much wealth as the bottom half of the US population, or 160 million people.

Analysis of the wealth of America’s richest people found that Gates, Bezos and Buffett were sitting on a combined $248.5bn (£190bn) fortune. The Institute for Policy Studies said the growing gap between rich and poor had created a “moral crisis”.

In a report, the Billionaire Bonanza, the thinktank said Donald Trump’s tax change proposals would “exacerbate existing wealth disparities” as 80% of tax benefits would end up going to the wealthiest 1% of households.

“Wealth inequality is on the rise,” said Chuck Collins, an economist and co-author of the report. “Now is the time for actions that reduce inequality, not tax cuts for the very wealthy.”

The study found that the billionaires included in Forbes magazine’s list of the 400 richest people in the US were worth a combined $2.68tn – more than the gross domestic product (GDP) of the UK.

“Our wealthiest 400 now have more wealth combined than the bottom 64% of the US population, an estimated 80m households or 204 million people,” the report says. “That’s more people than the population of Canada and Mexico combined.”

The report says the “billionaire class” continues to “pull apart from the rest of us” at the fastest rate ever recorded. “We have not witnessed such extreme levels of concentrated wealth and power since the first gilded age a century ago.”

Forbes celebrated 2017 as “another record year for the wealthiest people in America”, as “the price of admission to the country’s most exclusive club jumped nearly 18% to $2bn”. That was a tenfold increase on the amount of money needed to enter the list when it first started in 1982.

Josh Hoxie, another co-author of the thinktank report, said: “So much money concentrating in so few hands while so many people struggle is not just bad economics, it’s a moral crisis.”

The report says many Americans are joining an “emerging anti-inequality movement”. “A century ago, a similar anti-inequality upsurge took on America’s vastly unequal distribution of income and wealth and, over the course of little more than a generation, fashioned a much more equal America,” it says.

The rise at the wealthiest end of society comes as one in five US households live in what the report’s authors call the “underwater nation”, with either zero or negative wealth. Inequality is even more stark among minorities. Three in 10 black households and 27% of Latino ones have zero or negative wealth, compared with 14% of white families.

Just two African Americans made the Forbes 400: Oprah Winfrey (number 264 with $3bn) and the tech investor Robert Smith (226 with $3.3bn). Five members of the Forbes 400 have Latino backgrounds, including the property magnate Jorge Pérez, the LA Angels baseball team owner Arturo Moreno and three members of the family of late Colombian beer magnate Julio Mario Santo Domingo, a major shareholder of SABMiller.

The top 25 people in the survey are all white. The richest is Gates, the Microsoft founder, with $89bn, followed by Amazon’s Bezos with $81.5bn, then investor Warren Buffett with $78bn and Facebook’s Mark Zuckerberg with $71bn.

Since the Forbes 400 was published last month, Amazon’s share price has increased by more than 10%, lifting Bezos’s fortune to an estimated $95bn, putting him in the provisional number one spot.

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