US President Joe Biden moved swiftly on his first full day in the White House to fight the Covid-19 pandemic, his top priority as he turns the page on four years of Donald Trump's tumultuous leadership.

Biden signed a series of executive orders related to the pandemic on Thursday, he said the US death toll from the coronavirus will probably top 500,000 next month but vowed once again to move "heaven and earth" to get the "vaccine out the door as soon as possible" and inoculate 100 million Americans in 100 days.