US President Joe Biden will lead a remembrance ceremony Monday to mark the dark milestone of 500,000 American COVID-19 deaths.

With the US death toll on the brink of hitting half a million -- the highest impact on any country -- Biden ordered flags on federal government buildings to be flown at half mast for five days.

The president was scheduled to address the nation from the White House before attending a candle-lighting ceremony and moment of silence with wife Jill, Vice President Kamala Harris and her husband Doug Emhoff.

Unlike his predecessor Donald Trump, who often sought to minimize the disease, Biden has made the pandemic his top priority, simultaneously pushing an aggressive vaccine rollout and making frequent, public shows of empathy.

It is a strategy that could make or break the Biden presidency, already juggling high-stakes economic challenges and the tense political aftermath of the Trump era.

Biden has warned that the US toll could still go "well over" 600,000. But signs are also emerging that progress is being made both in the United States and around the world, with infections dropping sharply and vaccine deliveries rising steadily.