Half of all US adults will have received full Covid-19 vaccines on Tuesday, the White House said, marking another huge milestone in the fight against the pandemic.

"Today, the United States will reach 50 percent of American adults fully vaccinated," a White House official said, speaking on condition of anonymity.

More than half a million Americans have died from the coronavirus but the country is now a world leader in rolling out vaccinations.

The US has reached almost 50 percent of its population of 332 million with at least one dose, but its vaccination campaign is slowing in the face of hesitancy.

President Joe Biden has set a target of having 70 percent of adults vaccinated with at least one dose by July 4. The current figure is almost 62 percent.