French President Emmanuel Macron, who is hosting the summit, also weighed in, saying trade tensions were 'bad for everyone'.
British Prime Minister Boris Johnson said Saturday that he was "very concerned" about the trade tensions between the US and China, saying their tit-for-tat tariff hikes were harmful for the global economy.
"I'm very worried about the way it's going, the growth of protectionism, of tariffs that we're seeing," Johnson said as he arrived at the G7 summit in the French resort of Biarritz, where he was to make his full international debut as Britain's premier.
"Those who support tariffs are at risk of incurring the blame for the downturn in the global economy," he said. "This is not the way to proceed."
The question of tariffs is of particular concern for Johnson as he prepares to lead Britain out of the EU with the prospect of a no-deal Brexit on October 31 looking increasingly likely -- which experts warn would cost both sides dearly.
His remarks echoed earlier warnings from the European Union, which warned that the escalating trade spat between Washington and Beijing could drive economies around the world into recession.
"Trade wars will lead to recession, while trade deals will boost the economy," EU President Donald Tusk as G7 leaders descended on Biarritz for a three-day summit.
French President Emmanuel Macron, who is hosting the summit, also weighed in, saying trade tensions were "bad for everyone".
"We have to achieve some form of de-escalation, stabilise things, and avoid this trade war that is taking place all over," he said, just hours after Trump threatened to impose heavy punitive tariffs on France over its tax on US tech giants.
Trade disputes appear set to dominate the agenda of this year's G7 summit, with Tusk and Macron warning that an ambitious deal between the EU and Latin America's Mercosur bloc was at risk over Brazil's response to wildfires in the Amazon.
But Tusk also said the EU would respond in kind if the US imposed tariffs on French wine.