Joe Biden has signed 10 executive orders aimed at curbing the spread of coronavirus across the United States.
On his first full day in office, the newly-inaugurated president launched new measures on vaccines, masks and testing.
He hit out at Donald Trump’s handling of the coronavirus pandemic, saying his predecessor’s administration lacked the “urgency, focus and co-ordination we needed”.
“We have seen the tragic cost of that failure,” Mr Biden said.
He warned that “things are going to continue to get worse before they get better”, predicted the death toll will reach 500,000 next month and branded the country’s vaccine roll-out a “dismal failure”.
The US has seen the highest number of COVID-19 cases and deaths of any nation across the world.
So far there have been 408,011 fatalities and 24,538,028 infections in the country, according to Johns Hopkins University.
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Mr Biden addressed the stark figures in a ceremony on Thursday before he signed the executive orders.
“To date, more than 24 million Americans have been infected,” he said.
“To put that in context, America makes up 4% of the world’s population – but 25% of the world’s confirmed COVID-19 cases, and nearly 20% of all the COVID-19 deaths.”
The new measures include a requirement for everyone flying to the US to get a negative test result before they depart and then quarantine on arrival, and making it mandatory for Americans to wear face masks on public transport.
Other directives call for stronger safety protections for workers to prevent them catching coronavirus, and launching a new board to oversee the ramping up of testing.
But steep obstacles face the new president, with political uncertainty over whether Republicans in Congress will help him pass a $1.9tn (£1.3tn) relief package.
“We’re still in a dark winter of this pandemic,” Mr Biden said, adding progress will “take time”.
Mr Trump, who left the White House for Florida on Wednesday, was much-criticised for his handling of the pandemic.
He caught the disease in October, after hosting a reception where attendees were seen not social distancing or wearing masks.
And when a US journalist said Mr Trump told him he knew how dangerous the virus was but liked “playing it down”, former first lady Michelle Obama accused him of trying to “gaslight the American people by acting like this pandemic is not a real threat”.