Donald Trump has announced a 60-day ban on immigrants seeking to live and work in America permanently, and said he could extend it depending on the economic fallout from the coronavirus pandemic.

The US president framed the executive order, which he expects to sign on Wednesday, as an effort to protect American workers from foreign competition. He said it would apply only to those seeking green cards and not temporary workers, but he did not explain how those whose applications are currently being processed would be affected.

“By pausing immigration, we will help put unemployed Americans first in line for jobs as America reopens – so important,” Trump told reporters at Tuesday’s coronavirus taskforce briefing. “It would be wrong and unjust for Americans laid off by the virus to be replaced with new immigrant labour flown in from abroad. We must first take care of the American worker.”

The “pause” would be in effect for 60 days, he added, after which the need for an extension or alternation would be reviewed “based on economic conditions at the time”. Under questioning, he confirmed that he might then decide to add a further 30 days or more.

Trump said: “This order will only apply to individuals seeking a permanent residency. In other words, those receiving green cards. Big factor. It will not apply to those entering on a temporary basis ... We want to protect our US workers and I think, as we move forward, we will become more and more protective of them.”

The president, who has long campaigned against illegal immigration and again touted his US-Mexico border wall at Tuesday’s briefing, added that the move would help conserve medical resources for US citizens.

About a million people were granted green cards last year. The biggest share are family-based immigration sponsorships for permanent residency of foreign nationals by their American spouses. Alexander Hunter-Mihalić, a CNN producer, tweeted: “My wife’s greencard renewal is being – or was being – processed. What does that mean for her?”

The remarks followed an ambiguous tweet on Monday night that caught his own officials by surprise and provoked an angry backlash from immigration rights groups and Democrats.

Joe Biden, the presumptive Democratic nominee to take on Trump in November’s election, said: “Rather than execute a swift and aggressive effort to ramp up testing, Donald Trump is tweeting incendiary rhetoric about immigrants in the hopes that he can distract everyone from the core truth: he’s moved too slowly to contain this virus, and we are all paying the price for it.”

Facebook Twitter Pinterest A supermarket in Miami, Florida. Many immigrants are working in essential roles that keep the US operating amid the virus. Photograph: Joe Raedle/Getty Images

Ali Noorani, president of the National Immigration Forum, said: “President Trump’s call to suspend immigration to the US ignores the reality of our situation: the fact is that immigrants are standing shoulder to shoulder with US citizens on the frontlines helping us get through this pandemic. How many families would go without health care, food or otherwise if it wasn’t for immigrants working alongside native-born Americans yesterday, today and tomorrow?”

Immigrants account for 17% of healthcare workers and 24% of direct care workers nationwide, Noorani added, while H-1B visa holders are helping to find a vaccine to Covid-19 and agricultural workers continue to be essential in maintaining food chains that re-supply grocery stores.

Mayra Macías, executive director of Latino Victory, said: “Trump is once again using his old playbook of scapegoating immigrants to cover up his failures. But we will not be fooled – he’s doing it to distract us from his disastrous response to the coronavirus pandemic.”

In practice, much of the US immigration system has already been paralysed by the pandemic. Travel from China, parts of Europe and Iran is mostly banned and most state department visa services are suspended. The administration has used the crisis to effectively end asylum at US borders, including turning away children who arrive by themselves and putting a hold on refugee resettlement.

At Tuesday’s briefing Trump was also questioned about a malaria drug that he has been pushing relentlessly as a therapy for coronavirus, championing a Democratic state representative in Michigan who claimed it benefited her and frequently imploring: “What do you have to lose?”

Hydroxychloroquine: how an unproven drug became Trump’s coronavirus 'miracle cure' Read more

An analysis showed that nearly a third of military veterans died when treated with hydroxychloroquine, more than patients who received standard treatment. The president appeared to shrug off the finding, saying: “Obviously there have been some very good reports. Perhaps this one’s not a good report but we’ll be looking at it.”

Dr Stephen Hahn, the Food and Drug Administration’s commissioner, cautioned against drawing firm conclusions from the 368-patient sample. “This study is a small retrospective study at the VA [Veterans Affairs],” Hahn said. ‘This is something that a doctor would need to consider as part of a decision in writing a prescription for hydroxychloroquine.”

Earlier on Tuesday Trump hosted Andrew Cuomo, the governor of New York, at the White House, with testing top of the agenda. He said they agreed that the hospital ship USNS Comfort was no longer required by the state. “I’ve asked Andrew if we could bring the Comfort back to its base in Virginia so that we could have it for other locations and he said we would be able to do that.

“We’ll be bringing the ship back at the earliest time and we’ll get it ready for its next mission, which will I’m sure be a very important one also. But it was an honour.”

The US has 823,786 confirmed cases of the virus, and 44,999 deaths, according to the Coronavirus Resource Center at Johns Hopkins University. More than 4 million people have been tested.