US President Joe Biden said on Thursday that a donation of 500 million doses of the Pfizer Covid-19 vaccine to the world's poorest countries would supercharge the battle with the virus and comes with "no strings attached."

"The United States is providing these half billion doses with no strings attached. No strings attached," Biden said. "Our vaccine donations don't include pressure for favours, or potential concessions. We're doing this to save lives."

"America will be the arsenal of vaccines in our fight against COVID-19, just as America was the arsenal of democracy during World War Two," Biden said.

Biden, speaking alongside Pfizer Chief Executive Albert Bourla in the English seaside resort of Carbis Bay ahead of a G7 summit, thanked other leaders for recognising their responsibility to vaccinate the world.