Donald Trump has bowed to overwhelming pressure and invoked a national security law compelling General Motors to mass produce breathing equipment as the US becomes the first country to top 100,000 confirmed coronavirus cases.

But at yet another turbulent press conference, the president continued to give conflicting signals, claiming that more than 100,000 ventilators would be produced quickly but then casually suggesting some could be donated to the UK and other countries.

Challenged over whether everyone who needs a ventilator will get one, an agitated Trump snapped at a reporter: “Don’t be a cutie-pie. Everyone who needs one?” He also hurled abuse at state governors and complained bitterly that he feels unappreciated by them.

For weeks the president seemed reluctant to enforce the Defense Production Act (DPA), which grants him power to require companies to expand industrial production of key materials or products. He claimed it smacked of nationalising free enterprise and even drew comparisons with the socialist government of Venezuela.

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But officials say he did use it on 18 March, when he signed an order prioritising contracts and allocating resources to the US health secretary, Alex Azar, and again on 23 March, when he signed an order to prevent people from hoarding health and medical resources.

The third instance, an order compelling GM to begin manufacturing ventilators, was the most far-reaching as Trump came under criticism from state governors, Democrats and doctors for playing down a nationwide shortage of ventilators. “GM was wasting time,” Trump said in a statement. “Today’s action will help ensure the quick production of ventilators that will save American lives.”

Covid-19 is a respiratory illness. Most who contract it recover but it can be fatal, particularly among older people and those with underlying health problems. Ventilators enable a person with compromised lungs to keep breathing.

Some observers suggested Trump had acted out of spite after a long feud with GM. At the White House, he complained that “we thought we had a deal” with GM “and I guess they thought otherwise. They didn’t agree, and now they do … We let them know the way we felt and they can’t be doing that.”

He went on to list a series of grievances with GM, including its building of plants outside the US, adding: “We thought we had a deal for 40,000 ventilators, and all of a sudden it became six, and then price became a big object … We didn’t want to play games with them.”

The moved followed a series of tweets earlier on Friday in which Trump lambasted GM’s chief executive and its closure and sale of a car assembly plant in Lordstown, Ohio. This stood in sharp contrast to a message sent in May last year, praising the decision to sell.

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After Trump invoked the act, GM said it had been working around the clock for more than a week with Ventec Life Systems, a medical device company, and parts suppliers to build more ventilators. The company’s commitment to build Ventec’s ventilators “has never wavered”, it said.

Trump also announced that the White House trade adviser Peter Navarro would become the national DPA policy coordinator for the federal government. Navarro has been a leading advocate of Trump’s protectionist trade agenda, championing tariffs against China and the European Union.

Navarro told reporters: “We cannot afford to lose a single day, particularly over the next 30 to 60 days.”

The House speaker, Nancy Pelosi, welcomed Trump’s use of the DPA as “an important but seriously belated step”. She added in a statement on Friday: “Much more must be done. The president must use the full powers of this law to address the dire, widespread shortage of materials required to fight this pandemic, including diagnostic test supplies, masks and other personal protective equipment.”

Critics say Trump ignored early warnings about the threat of the pandemic and had he acted sooner, mass production of ventilators would now be well under way. The New York Times reported estimates that if the White House had reacted to the shortage in February, the private sector might have had them ready in mid- to late April; instead it is now unlikely to be before June.

Trump’s call for the building of more ventilators comes one day after he expressed scepticism about New York Governor Andrew Cuomo and medical experts’ prediction that his state would need 30,000 to 40,000 ventilators when the coronavirus outbreak peaks there.

On Friday Trump refused to back down on his comments, saying: “I think their estimates are high. I hope they’re high.”

He suggested the ventilators produced by GM and others would serve not only New York but other parts of the US was well as helping the UK, Italy, Germany and Spain. When he called Boris Johnson, the British prime minister, who has tested positive for the virus, Johnson immediately said, “We need ventilators,” Trump recalled. “We’ll take care of our needs but we’re also going to take care of other countries.”

During Friday’s briefing, Trump also lashed out at state governors. “All I want them to do, very simple, I want them to be appreciative. I don’t want them to say things that aren’t true. I want them to be appreciative. We’ve done a great job.”

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He described Jay Inslee, the governor of Washington, as a “failed presidential candidate” and dismissively referred to Governor Gretchen Whitmer as “the woman in Michigan”.

Trump said of the vice-president, Mike Pence: “He calls all the governors. I tell him, I’m a different type of person, I say: ‘Mike, Don’t call the governor of Washington. You’re wasting your time. Don’t call the woman in Michigan.’ You know what I say? If they don’t treat you right, I don’t call.”

In another bizarre moment, when Trump was asked for a message to schoolchildren forced to stay at home, he said: “You can call it a germ, a flu, a virus, you can call it many things. I’m not sure people know what it is.” Scientists have identified it as coronavirus disease (Covid-19), an infectious disease caused by a newly discovered coronavirus called Sars-CoV-2.

In another sign that Trump is not living up to his appeal for bipartisanship, Trump did not invite Pelosi or any other Democrats to the signing of a $2.2tn emergency relief bill. Pelosi said in a statement on Friday: “We must do more to address the health emergency, mitigate the economic damage, and provide for a strong recovery.”