Donald Trump has extended America’s national shutdown for a month, bowing to public health experts, and scientific reality, and warning that the worst of the coronavirus pandemic is yet to come.

Speaking in the White House Rose Garden, the US president claimed that, if his administration keeps the death toll to 100,000, it will have done “a very good job” – a startling shift from his optimistic predictions of a few days ago when he said he hoped to restart the economy by Easter.

Trump also undermined his plea for unity by uttering falsehoods, verbally abusing reporters and making incendiary allegations that implied health care workers were stealing masks, without providing evidence.

The extended deadline marked a humiliating retreat for the president who, having squandered six precious weeks at the start of the pandemic, more recently complained that the cure is worse than the problem and floated Easter Sunday as a “beautiful timeline” for reopening big swathes of the country.

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On Sunday he claimed this had only been “aspirational” as his advisers urged him not to move too hastily. He announced the initial 15-day period of social distancing urged by the federal government, which was due to expire on Monday, would be extended to 30 April, and said he hoped normality might return by 1 June.

The guidelines recommend against big group gatherings and urge older people and anyone with existing health problems to stay at home. People were also urged to work at home when possible and avoid restaurants, bars, non-essential travel and shopping trips.

“The modelling estimates that the peak in death rate is likely to hit in two weeks,” Trump told reporters, with the toll already at more than 2,400. “Nothing would be worse than declaring victory before the victory is won. That would be the greatest loss of all.”

He added: “We can expect by June 1st we will be well on our way to recovery.”

The shift came as the full horror of the pandemic appeared to dawn on a president who long downplayed it. Dr Anthony Fauci, the government’s top infectious disease expert, said the US could experience more than 100,000 deaths and millions of infections. Fauci praised the extension as a “wise and prudent” decision.

Trump cited projection models that said potentially 2.2 million people or more could have died had the country tried to “wing it” and not put social distancing measures in place. “I kept asking and we did models,” he said. “These are 2.2 million people would have died.

“And so, if we could hold that down, as we’re saying, to 100,000 – it’s a horrible number, maybe even less, but to 100,000, so we have between 100 [thousand] and 200,000 – we altogether have done a very good job.”

Facebook Twitter Pinterest Health care workers stand outside a tent erected to test people for the Covid-19 at the Elmhurst Hospital Center in Queens, New York City. Photograph: Andrew Kelly/Reuters

Trump also appeared to have been rattled by scenes at Elmhurst Hospital where he grew up in Queens, New York. “I’ve been watching that for the last week on television,” he said. “Body bags all over, in hallways.”

“I’ve been watching them bring in trailer trucks, freezer trucks, they’re freezer trucks, because they can’t handle the bodies, there are so many of them. This is essentially in my community, in Queens; Queens, New York. I’ve seen things that I’ve never seen before.”

Trump had minimised the threat of the coronavirus for weeks and ignored the pleas of his health secretary to investing in testing kits and breathing apparatus. The House Speaker, Nancy Pelosi, told CNN’s State of the Union this attitude had cost American lives. “The president, his denial at the beginning, was deadly,” she said.

Play Video 1:02 'As the president fiddles, people are dying': Nancy Pelosi slams Trump's coronavirus delays – video

Trump has long been criticised for refusing to own up to his own mistakes and shifting blame to others. In another lengthy, abrasive press conference, he pushed a conspiracy theory speculating that hospital staff may be stealing N95 masks and selling them on the black market.

The current demand does not square with what hospitals usually use, he told reporters. “It’s a New York hospital, very – it’s packed all the time. How do you go from 10 to 20 [thousand masks per week] to 300,000? Ten [thousand] to 20,000 masks, to 300,000 – even though this is different? Something is going on, and you ought to look into it as reporters. Are they going out the back door?”

He added: “How do you go from 10,000 to 300,000? And we have that in a lot of different places. So somebody should probably look into that, because I just don’t see from a practical standpoint how that’s possible to go from that to that.”

When a reporter asked the president to clarify, he asked for New York Governor Andrew Cuomo and Mayor Bill de Blasio to investigate, adding: “I don’t think it’s hoarding. I think it’s maybe worse than hoarding.”

The comments provoked widespread outrage. Joe Kennedy III, a Democratic Congressman from Massachusetts, tweeted: “We need supplies. We need masks. Our frontlines are suffering. Suggesting otherwise is disgusting.”

Joe Biden, the front runner for the Democratic presidential nomination, said: “This is ridiculous and completely false. Today’s conspiracy mongering from our president is among the most reckless and ignorant moves he has made during this crisis, and there have been many. Lives hang in the balance.”

Facebook Twitter Pinterest A White House aide attempts to take the microphone out of the hands of PBS NewsHour correspondent Yamiche Alcindor as she questions Donald Trump. Photograph: REX/Shutterstock

As in previous briefings all week, the president picked fights with individual reporters including Yamiche Alcindor, a reporter at PBS NewsHour who is a woman of colour.

When Alcindor questioned him about comments he made during an interview with Fox News’s Sean Hannity that suggested state governors were making exaggerated demands, Trump retorted: “Why don’t you act in a little more positive? ... It’s always get ya, get ya, get ya. You know what? That’s why nobody trusts the media anymore.”

He added: “Look, let me tell you something, be nice. Don’t be threatening. Be nice.”