WASHINGTON (BLOOMBERG) - US President Donald Trump clashed with Democrat Joe Biden over requirements to wear masks to prevent the spread of the coronavirus.

Mr Biden said Thursday (Aug 13) that every governor should require masks for the next three months, an approach he said would save more than 40,000 lives.

In June, Mr Biden has said that as president he'd "insist" that every American wear a face covering and use his executive powers to enact a requirement.

"Every single American should be wearing a mask when they are outside for the next 3 months at a minimum," Mr Biden told reporters in Delaware. "It's not about your rights, it's about your responsibilities as an American."

Mr Trump rejected Mr Biden's approach on Thursday.

"If the president has the unilateral power to order every single citizen to cover their face in nearly all instances, what other powers does he have?" Mr Trump said. "We want to have a certain freedom, that's what we're about."

Mr Trump's views on executive power over the pandemic response have constantly shifted. The president claimed in April he had "total" authority over whether states re-open their economies, before walking it back and saying that was the governors' responsibility.

The clash highlights a surge in coronavirus cases in the US, and criticism the president has faced over whether he's acted forcefully enough to slow its spread. The president has left it to governors to determine whether to require masks, resulting in a patchwork of requirements in the US.

Some public health experts have said a national mask mandate would slow the spread of the virus while others have questioned whether a requirement would spark a backlash. The virus has killed more than 166,000 people in the US.

Mr Trump generally doesn't wear masks in public but has urged Americans to do so when they can't maintain adequate distance from one another.

"I emphasised this is a patriotic thing to do," Mr Trump said of wearing a mask. "Maybe they're great and maybe they're just good. Maybe they're not so good. But frankly, what do you have to lose?"