Trump paints picture of unity at prickly G7 summit

US President Donald Trump on Sunday said he was getting along well with his Western allies at a G7 summit in France, dismissing reports of rifts among leaders as they prepared to discuss global trade woes.

The G7 gathering is taking place against a backdrop of growing worries about a global economic downturn and coincides with an era of international disunity across an array of issues that have strained decades-old allegiances.

"Before I arrived in France, the Fake and Disgusting News was saying that relations with the 6 others countries in the G-7 are very tense, and that the two days of meetings will be a disaster," Trump wrote on Twitter shortly before meeting British Prime Minister Boris Johnson.

"Well, we are having very good meetings, the Leaders are getting along very well, and our Country, economically, is doing great - the talk of the world!"

However, major policy differences over trade protectionism, climate change, Iran and France's push for a universal tax on digital technology giants clouded the run-up to the summit in the Atlantic coastal resort of Biarritz.

Trump arrived in France just hours after escalating his trade war with China in a tit-for-tat battle between the world's two largest economies that has spooked financial markets.

"I am very worried about the way it's going, the growth of protectionism, of tariffs that we're seeing," the UK's Johnson said on Saturday.

"Those who support the tariffs are at risk of incurring the blame for the downturn in the global economy, irrespective of whether or not that is true."

Underlining the discord, Trump also threatened his host on the eve of the summit, saying the United States would tax French wine "like they've never seen before" unless Paris dropped a digital tax on US technology companies.

Leaping into the fray, European Council President Donald Tusk, who takes part in the G7 discussions, warned the EU would respond "in kind" if Trump acted on his threat.

"This may be the last moment to restore our political community," Tusk told reporters on Saturday, giving a bleak assessment of Western relations.

Looking to broaden the scope of the debate, Macron has invited several African leaders to discuss the problems facing their continent, while leaders from India, Australia, Chile and Spain are due to attend a dinner on Sunday where the focus will be on the environment and other issues.