Donald Trump was warned at the end of January by one of his top White House advisers that coronavirus had the potential to kill hundreds of thousands of Americans and derail the US economy, unless tough action were taken immediately, new memos have revealed.

The memos were written by Trump’s economic adviser, Peter Navarro, and circulated via the National Security Council widely around the White House and federal agencies.

They show that even within the Trump administration alarm bells were ringing by late January, at a time when the president was consistently downplaying the threat of Covid-19.

According to figures from Johns Hopkins University in Maryland, by Tuesday more than 368,000 cases of Covid-19 had been confirmed in the US and more than 11,000 people had died. New York is the hardest-hit state: on Tuesday the governor, Andrew Cuomo, said the death toll was nearly 5,500, after the biggest single-day increase.

More than 1,000 have died in New Jersey and more than 700 in Michigan. California and Louisiana are also leading hotspots.

As Cuomo spoke, and as reports about the Navarro memos dominated media coverage, Trump tweeted angrily.

The president complained about the World Health Organization and a report by a federal health department watchdog which details serious problems faced by US hospitals dealing with the pandemic.

“The WHO really blew it,” Trump wrote. “For some reason, funded largely by the United States, yet very China centric. We will be giving that a good look. Fortunately I rejected their advice on keeping our borders open to China early on. Why did they give us such a faulty recommendation?”

The WHO has cautioned against travel bans, saying they are not effective and can be counterproductive. In January, two days after the first Navarro memo, Trump placed restrictions on travel from China but did not totally close it down, as he has repeatedly claimed. The president’s complaint on Tuesday was resonant of attacks on other international bodies including Nato and the World Trade Organization.

Trump also attacked the office of the inspector general for the Department of Health and Human Services at his White House briefing on Monday.

On Twitter on Tuesday, he asked: “Why didn’t the IG, who spent [eight] years with the Obama administration (Did she Report on the failed H1N1 Swine Flu debacle where 17,000 people died?), want to talk to the Admirals, Generals, VP & others in charge, before doing her report. Another Fake Dossier!”

The official in question, Christi Grimm, is principal deputy inspector general and has worked for the health department since 1999, serving under Bill Clinton, George W Bush, Barack Obama and now Trump.

Trump has regularly attacked Obama for his handling of public health matters including the outbreak of H1N1, or swine flu, in 2009. The US Centers for Disease Control and Prevention says about 12,500 Americans died in that episode.

Trump’s reference to a “fake dossier” echoed his complaints about political opposition research work carried out by a former British intelligence officer, Christopher Steele, and subsequently at the heart of the investigation of Russian election interference and links between Trump and Moscow.

Trump fired the inspector general for the intelligence community, Michael Atkinson, on Friday night, over his role in sending to Congress a whistleblower complaint about Trump’s approaches to Ukraine which led to the president’s impeachment.

The Navarro memos, first reported by the New York Times and Axios, were written by Navarro on 29 January and 23 February. The first memo, composed on the day Trump set up a White House coronavirus task force, gave a worst-case scenario of the virus killing more than half a million Americans.

According to the Times, it said: “The lack of immune protection or an existing cure or vaccine would leave Americans defenseless in the case of a full-blown coronavirus outbreak on US soil. This lack of protection elevates the risk of the coronavirus evolving into a full-blown pandemic, imperiling the lives of millions of Americans.”

The second memo went even further, predicting that a Covid-19 pandemic, left unchecked, could kill 1.2 million Americans and infect as many as 100 million.

This was not the first time Trump and his White House team were warned that the virus had the potential to devastate the US and needed to be dealt with quickly and firmly.

Senior scientists, epidemiologists and health emergency experts in the US and around the world delivered that clear message early on in the crisis, only for Trump to continue belittling the scale of the threat which he compared falsely to the dangers of seasonal flu.

But the emergence of the memos from such a senior aide within the White House will make it much more difficult for Trump to claim – as he has done on multiple occasions – that nobody was able to predict the severity of the disease.

As the pandemic has swept across the country, the president has come under mounting criticism for having done too little, too late in response, leading to mass shortages of diagnostic testing, protective gear for frontline health workers and ventilators for the very sick.