But the American economy is in trouble as an additional 5.2 million people filed for unemployment benefits last week, with a historic 22 million Americans having filed jobless claims in the last month alone.

Trump used his briefing to back off from recent conflicts with governors. “We’ve had a great relationship, Democrat, Republican the relationship has been good,” he said and emphasised their role in the process of reopening.

“My administration is issuing new federal guidelines that will allow governors to take a phased and deliberate approach to reopening their individual states,” said Trump.

Trump explicitly left the time table for opening up their states to the governors.

“Governors will be empowered to tailor an approach that meets the diverse circumstances they have in their own states,” he said. “If they need to remain closed we will allow them to do that. And if they believe it is time to reopen, we will provide them the freedom and guidance to accomplish that task and very, very quickly.”

Before the phases can be initiated, states must meet a series of “gating criteria” including a downward trajectory of confirmed cases and cases of patients with Covid-19 symptoms over a 14-day period.

During phase one vulnerable populations continue to shelter at home, outside the home social distancing is still practiced and gathering in groups of more than ten people is not allowed. Schools remain closed but restaurants and other gathering places can operate only while enforcing strict physical distancing protocols.

In phase two, gatherings of more than 50 people are discouraged, but non-essential travel can resume. Schools can reopen and large venues including restaurants can operate with only moderate physical distancing.

Phase three represents a return to what is being called the “new normal” - going about normal life with a focus on good hygiene, hand-washing and keeping as much space as possible between people when outside the home and with everyone avoiding crowds wherever possible.

None of the phases have timelines from the federal government, with the timing of their rollout left to the discretion of governors.

“Constant sentinel surveillance in communities with large numbers of vulnerable populations” will be a key part of the opening strategy, said White House coronavirus response coordinator Dr Deborah Birx, explaining that these outposts run by the Centres for Disease Control and Prevention in conjunction with local health authorities will test anyone coming to clinics, regardless of what they are seeking treatment for.

Lawmakers and medical experts agree that one of the largest roadblocks to reopening the economy is the country’s limited testing capacity. Since most communities are unable to offer comprehensive tests, they argue that citizens will be afraid to go back to work, and that the government would be hobbled in responding quickly if infections spiked unexpectedly.

Birx said her team and the Centres for Medicare and Medicaid Services are working with labs at universities and other institutions to create capacity to run an additional 1 million Covid-19 tests per week.

Still, some expect setbacks.

A spike in cases is almost inevitable in a state like California because of a large number of homeless people, said Kate Zaiger, a Sacramento-based medical adviser to state Governor Gavin Newsom.

“It’s a bigger crisis than what we’re seeing, and if they want to reopen, fine, but it’s not going to end well,” Zaiger said, pointing out that there are numerous homeless camps in the state with no running water to wash hands or enough separation between those living in them.

Site launched in US to track coronavirus-inspired hate speech and abuse

California, America’s most populous state, has a homeless population of about 150,000, according to US government data.

While Trump stayed away from the kind of political attacks that have characterised the daily White House press briefing, blame over who is more responsible for the spread of Covid-19 spilled out elsewhere.

Just hours before Thursday’s briefing, Trump suggested in a Twitter post that House Speaker Nancy Pelosi, a Democrat, was “responsible for many deaths” for encouraging people on February 24 to visit San Francisco’s Chinatown, three weeks before the city issued stay-at-home orders.

Trump himself has come under fire from Democrats for downplaying the Covid-19 threat well into March, before ultimately endorsing strict social distancing guidelines.

Additional reporting by Robert Delaney