World leaders are set to open a two-day Group of 20 summit in Argentina on Friday, with global trade concerns set to dominate, while the flare up in Russia-Ukraine tensions and the fallout from the murder of Saudi dissident Jamal Khashoggi are also likely to feature.

While there have been some signs that Chinese and US delegations could reach a ceasefire on trade, there are growing worries that President Donald Trump and President Xi Jinping will not be able to make a breakthrough at their highly-anticipated meeting at the summit.

Before departing Washington on Thursday, Trump said he was "very close" to reaching a deal with China but added "I don't know that I want to do it because what we have right now is billions and billions of dollars coming into the United States in the form of tariffs or taxes."

Trump said China "wants to make a deal," and was open to one, but said he liked "the deal we have right now."

The US began hiking tariffs on Chinese goods earlier this year and Beijing has responded in a tit-for-tat fashion, sparking tensions that a full trade war could erupt.

Trump has already threatened to further increase tariffs on some 200 billion dollars worth of Chinese goods.

Ottawa meanwhile confirmed the new trade deal between Canada, the US and Mexico would be signed in Buenos Aires on Friday. However the United States-Mexico-Canada Agreement (USMCA) will still need ratification from each country's legislative body.

Following the G7 summit in Canada in June, Trump triggered a war of words with Prime Minister Justin Trudeau, calling him "dishonest," and withdrawing support for a joint G7 communique, after the Canadian leader vowed retaliation for US tariffs on steel and aluminium.

The recent flare up of tensions between Ukraine and Russia is also likely to loom large at the summit, with Trump abruptly cancelling a planned meeting with Russian President Vladimir Putin on his way to the summit.

"Based on the fact that the ships and sailors have not been returned to Ukraine from Russia, I have decided it would be best for all parties concerned to cancel my previously scheduled meeting ... in Argentina with President Vladimir Putin," he tweeted from Air Force One.

On Sunday, Russia seized three Ukrainian naval vessels off the Crimea Peninsula, a territory it annexed from Ukraine in 2014.

Saudi Arabia's Crown Prince Mohammed bin Salman is also attending the summit, though it remains to be seen how warmly he will be welcomed by other leaders following the murder of journalist Jamal Khashoggi at the Saudi consulate in Istanbul last month.

The crown prince is suspected of ordering the October killing of Khashoggi in the Saudi consulate in Istanbul. Saudi Arabia has denied the charges and the White House says there is no smoking gun tying the crown prince to the murder.

When asked about why he had no plans to meet the crown prince in Buenos Aires, Trump said before boarding his plane he would have been happy to meet him but did not have time.

"I would have met with him but we didn’t set that one up," he said.

Representatives of the G20 nations, who make up more than 80 per cent of the world's economy and global trade, have already been working this week on a joint statement to close the summit, in the hopes all sides can agree on wording.

The language on open and fair trade in any final statement will be closely watched.