Biden landed in England on Wednesday for the start of his first foreign trip as president -- which features the G7 meeting, summits with NATO and the European Union in Brussels, and finally talks with Putin in Geneva.

On the way, Biden's national security advisor, Jake Sullivan, told reporters aboard Air Force One that the president would kick things off with news of a major vaccine sharing initiative.

Sullivan would not give full details, but according to US media reports, the Biden administration is set to buy 500 million doses of the Pfizer/BioNTech vaccine for international distribution.

Doses will be aimed at developing countries, Sullivan said.

"The president is focused on helping to lead the world because he believes it's the right thing to, it's what Americans do in times of need," he said.

"We were the arsenal of democracy in World War II. We're going to be the arsenal of vaccines."

The Group of Seven will make a further joint declaration on "a comprehensive plan to help end this pandemic as rapidly as possible," Sullivan said.

- 'Tight' transatlantic ties -

The 78-year-old president was headed first to the G7 gathering in a Cornish seaside resort from Friday to Sunday, alongside the leaders of Britain, Canada, France, Germany, Italy and Japan.

From there, in rapid succession, he will visit Queen Elizabeth II at Windsor Castle and fly to Brussels for summits with the NATO military alliance on Monday and the European Union on Tuesday. He will finish in Geneva to meet Putin next Wednesday, holding talks in an elegant villa overlooking Lake Geneva, a US official who asked not to be named told AFP.

With the world still crawling out from under the wreckage of Covid-19, Biden has cast his diplomatic marathon as a return to badly needed US leadership.

Boarding Air Force One outside Washington earlier Wednesday, Biden said his trip would make "clear to Putin and China that Europe and the United States are tight."

Biden's pitch marks a return to traditional US diplomacy after four years during which Donald Trump flirted with autocrats and recast multilateralism as a dirty word.

- 'Wind at back' -

That's a message that the trip's choreography, with Biden meeting a Who's Who of US allies before sitting down with Putin, reinforces.

"He will go into this (Putin) meeting with the wind at his back," Sullivan said.

But European partners, still reeling from Trump shock, may eye Biden's vows with some scepticism.

As Biden departed Washington, the European Union trade commissioner, Valdis Dombrovskis, called on the US to "walk the talk" when it comes to resolving lingering Trump-era trade disputes.

And there was friction last month when Washington blocked French attempts at the United Nations to demand a ceasefire between Israel and Hamas in Gaza.

Biden's ramping up of vaccine donations also follows what critics saw as a long period of hoarding.

Biden's meeting on the sidelines of NATO with Turkish President Recep Tayyip Erdogan promises to be especially prickly.

Biden has irked Erdogan, who was sometimes a Trump ally, by highlighting Turkey's dire human rights situation and recognising the Ottoman Empire's genocide against the Armenians. Washington risks "losing a precious friend," Erdogan has warned.

- 'More stable?' -

Expectations for the Putin summit are so low that simply making US-Russian relations "more stable" would be considered a success, Secretary of State Antony Blinken and other White House officials say.

The White House sees the extension of the New START nuclear arms treaty in February as an example of where business can be done. Biden also needs the Kremlin to make progress with Iran, which is close to Russia.

The list of tensions, however, is far longer.

Biden blames Russia for the massive SolarWinds cyberattack, election interference, and at the very least harbouring criminals behind ransomware attacks against the vital Colonial fuel pipeline and the US subsidiary of Brazilian meatpacking giant JBS.

Biden will also press Putin about sabre-rattling on the Ukrainian border, the imprisonment of opponent Alexei Navalny, and his support for Alexander Lukashenko, the Belarussian strongman who forced a Ryanair airliner to land in Minsk, then arrested an opponent on the flight.

It's a long to-do list for the US president on his first foreign trip.

But Press Secretary Jen Psaki said that with decades in the Senate and eight years as vice president under Barack Obama, Biden has done his homework.

"He's been getting ready for 50 years," she said.