Donald Trump urged Americans to refrain from panic buying basic supplies during the Covid-19 pandemic as the administration announced plans to expand testing for the virus and health officials were preparing to release “advanced guidelines” on how to mitigate its spread.

During a press briefing at the White House on Sunday evening, Trump again appeared to downplay the threat of the novel coronavirus. “Relax, we’re doing great,” he said, during short, meandering comments that focused mostly on celebrating a decision by the Federal Reserve to lower interest rates. “It all will pass.”

The president’s remarks stood in marked contrast to his lead infectious diseases expert, Dr Anthony Fauci, who used the same conference to warn: “The worst is ahead for us,” describing the crisis as reaching a “very, very critical point now”. Earlier in the day Dr Fauci had declined to rule out a “national lockdown” of bars and restaurants as he urged more aggressive measures, similar to those in Europe and elsewhere, to contain the virus.

Trump said he had hosted a call with grocery industry leaders earlier in the day who had pushed him to spread a message against hoarding.

“They have actually asked me to say: ‘could you buy a little bit less, please?’ I thought I’d never hear that from a retailer,” Trump said, adding: “They have no shortages. We have no shortages other than people buying anywhere from three to five times [more].

“Have a nice dinner, relax,” the president added.

Trump’s remarks came at the same time that California’s governor, Gavin Newsom, announced that the nation’s most populous state would enforce a closure of all bars and nightclubs, and make restaurants cut capacity by half. The governor also urged all those over 65 to self-isolate.

The Centers for Disease Control (CDC), the leading US government agency for public health, announced a national recommendation shortly after, urging all gatherings of 50 people or over, including festivals, parades, weddings and sporting events, to be cancelled for the next eight weeks. The recommendation did not include schools or businesses.

Twenty-four states have already announced some form of school closure, with Massachusetts becoming the latest to announce on Sunday. Governor Charlie Baker also banned gatherings of 25 people or more in the state.

Mike Pence, the vice-president and head of the president’s coronavirus taskforce, said on Sunday evening there were now 2,900 confirmed cases across 49 states in America, up from 2,200 on Saturday.

As the administration reels from criticism of its slow rollout of tests for coronavirus, Pence announced an ambitious new testing regimen, which he said would allow 1.9m Covid-19 tests to be processed over the coming weeks at over 2,000 laboratories across the country.

He said the new resources would “enable all Americans who need to be tested to go to a community-based testing site outside of usual healthcare facilities”.

Pence commended leaders in 10 states for already rolling out “drive-through” testing.

Dr Deborah Birx, the White House coordinator for responding to the pandemic, said those most vulnerable to the virus and the healthcare providers treating them should be tested first.

“We ask you to prioritize them and prioritize them in the lines,” she said, adding that the roll-out of more testing would lead to a “spike” in positive results.

The health and human services secretary, Alex Azar, described the crisis as “an unprecedented challenge” and acknowledged the pandemic carried the risk of overwhelming the healthcare system in the US. Azar said the administration was working to increase the number of medical supplies, including ventilators, available to fight the pandemic. But he declined to cite specific figures citing “national security”.

Dr Fauci said that new “advanced guidelines” on how to mitigate the spread of the disease would be announced on Monday but there was little more detail on recommended measures of “social distancing”, actions that limit interaction between people in order to prevent further contraction.

Earlier on Sunday, Melania Trump, the first lady who has remained largely absent from public since the onset of the crisis, tweeted a link to the CDC website and urged readers to “Please take action to prevent further spread.”