A US panel of independent experts has voted unanimously in favour of recommending Johnson & Johnson's one-dose Covid-19 shot for emergency approval, clearing the way for a third vaccine to soon begin shipping in the world's hardest-hit country.

The committee's 22 members were convened by the Food and Drug Administration and included leading scientists as well as consumer and industry representatives, according to AFP.

“We've all seen the news about (the) Johnson and Johnson vaccine today — (the) third, safe effective vaccine,” President Joe Biden said from Houston shortly after the vote.

“We're going to use every conceivable way to expand manufacturing of the vaccine ... and make even more rapid progress in getting (shots) to people's arms.”