Hospitals in the US could be overrun by coronavirus cases in little more than a week, a former Obama administration senior health official has warned, fearing a “tsunami-like” escalation that would leave tens of thousands in need of inpatient medical care but unlikely to receive it.

Andy Slavitt, who was Obama’s acting administrator of Medicare and Medicaid, said the trajectory of the spread of the virus in the US could follow that of Italy, which has seen cases soar to almost 20,000 and deaths exceed 1,300 in short order.

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The only way for the US to avoid such an explosion, Slavitt said in a series of tweets on Saturday, was for the entire population to follow a strict policy of social isolation and hospitals to reorganise and prioritise resources to fight the outbreak.

“Expanding medical capacity has to be done but will only make a tiny difference if we don’t self-isolate,” Slavitt said.

“I get it. Home from work. Cooped up. Crisis mentality. We need to let steam off. Shared experience. But stop that. All the bars and restaurants are closed now across Europe.”

Tweets by Slavitt on Friday highlighted some experts’ expectations that more than 1 million could die in the US from coronavirus, and that early inaction by the Trump administration had fueled “a major preventable public health disaster”.

“The original sin is Trump’s months-long denial and his dismantling of public health and response infrastructure,” Slavitt said.

“That wasn’t all, but it led to other fatal mistakes. The public health infrastructure could have been prepared. What does that mean: nasal swabs, respirators, ventilators, RNA kits to read tests, machines, gloves…”

Slavitt’s renewed warning on Saturday came as Trump appeared at the White House to outline the latest steps his administration was taking to try to contain coronavirus, including extending a European travel ban to the UK and Ireland and allocating $50bn in federal funding freed up on Friday by the declaration of a national emergency.

“By 23 March many of our largest cities and hospitals are on course to be overrun with cases,” Slavitt wrote, adding that he was preparing an advisory memo for state and local officials around the US to whom he had been speaking.

“They are highly dependent on the public response so I will start there. We have no immunity to Covid-19, people who get it don’t know it for a while, and each person that gets it, they infect 2+ people,” he wrote alongside a “lag tracker” graph showing the existing and predicted escalation rate of coronavirus in countries including the US, and photographs from hospitals in Italy.

“Every report describes this as a tsunami. And if it happens like a tsunami, in major cities we will have tens of thousands more cases than we have beds and we will have one ventilator for every eight people who need one.”

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Other medical experts have also warned the public to brace for an overwhelming number of coronavirus cases.

“We’re about to experience the worst public health disaster since polio,” said Dr Martin Makary, professor at Johns Hopkins University’s Bloomberg School of Public Health, speaking to Yahoo Finance.

“Don’t believe the numbers when you see, even on our Johns Hopkins website, that 1,600 Americans have the virus. No, that means 1,600 got the test, tested positive.

“There are probably 25 to 50 people who have the virus for every one person who is confirmed. I think we have between 50,000 and half a million cases right now walking around in the United States.”