The leaders of the world's largest economies opened talks on Friday overshadowed by US President Donald Trump’s threat to escalate tariffs on imports from China as well as military tensions between Russia and Ukraine.

This year’s two-day gathering is a major test for the Group of 20 industrialised nations, whose leaders first met in 2008 to help rescue the global economy from the worst financial crisis in seven decades.

With a rise in nationalist sentiment in many countries, the G20 — which accounts for two-thirds of the global population — faces questions over its ability to deal with trade tensions, which have roiled global markets, and ease geo-political disputes.

Hanging over the summit in Buenos Aires is the trade dispute between the US and China, the world’s two largest economies, which have imposed tariffs on hundreds of billions of dollars on each other’s imports.

Global financial markets will take their lead next week from the outcome of talks between Trump and Chinese President Xi Jinping over dinner on Saturday, aimed at resolving differences that are weighing on global economic growth. Beijing hopes to persuade Trump to abandon plans to hike tariffs on $200 billion of Chinese goods to 25 per cent in January, from 10 per cent at present.

Trump said on Friday there were some good signs for the talks with China ahead of his meeting with Xi.

Donald Trump with Narendra Modi and Shinzo Abe in Buenos Aires on Friday. AP

“We’re working very hard. If we could make a deal that would be good. I think they want to. I think we’d like to. We’ll see,” he said, speaking during a meeting with Japanese Prime Minister Shinzo Abe.

US trade representative Robert Lighthizer earlier told reporters that Trump and Xi have a good personal relationship and “I would be very surprised if it (their meeting) was not a success”.

“But in terms of doing a deal ... that’s entirely up to the President of the United States and the President of China. Way, way, way above my pay grade,” he said.

On the eve of the summit, G20 nations were still trying to reach consensus on wording for the summit’s communique on major issues including trade, migration and climate change, which in past years have been worked out well in advance.

Trump’s scepticism that global warming is caused by human activity has raised questions about whether the countries will be able to find enough common ground on climate change to include it in any communique.

Earlier this month, officials from countries attending a major Asia-Pacific summit failed to issue a joint statement for the first time after the US delegation clashed with China over trade and security.