US President Joe Biden (first left) and Vice President Kamala Harris (second right) hold a moment of silence for the dead due to COVID-19 at the White House on Monday. Photo: AFP

US President Joe Biden ordered flags lowered to half mast Monday after the US crossed the "heartbreaking" milestone of 500,000 COVID-19 deaths, while Britain eyed lifting lockdowns in the latest sign of global gains against the pandemic.

"I know what it's like," an emotional Biden said in a national television address, referring to his own long history of family tragedies.

"I ask all Americans to remember, remember those we lost and those they left behind," Biden said.

Biden, accompanied by his wife Jill and Vice President Kamala Harris and her husband Doug Emhoff, then stood outside the White House to mark a moment's silence in front of 500 candles representing the toll.

Earlier, flags were lowered over the White House and at federal buildings nationwide as well as at embassies around the world. 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 US and around the world, with infections dropping sharply and vaccine deliveries rising steadily.

In Britain, Prime Minister Boris Johnson outlined a "gradual and cautious" approach to lifting curbs in England that could see life there return almost to normal by the end of June. 

There was also good news from a University of Edinburgh study finding that Pfizer and Oxford-AstraZeneca vaccinations have led to a "substantial reduction" in COVID-19 admissions to hospitals in Scotland.

Despite the dramatic losses in the US, the trend there is also sharply downward.

Rochelle Walensky, director of the Centers for Disease Control and Prevention, said US deaths are at their lowest since December, with a 39 percent drop in the latest seven-day average of new daily cases.

AFP