Donald Trump has told Scott Morrison he has done "a fantastic job in a very short period of time" as prime minister.

The United States president has met Mr Morrison at the G20 in Argentina and the leaders spoke about trade in their first ever meeting.

“Australia and the United States have always been the greatest of friends” replies Prime Minister Scott Morrison #G20Summit #auspol @SBSNews pic.twitter.com/Q6xnWcBvVr — Brett Mason (@BrettMasonNews) November 30, 2018

"Just getting to know each other and so far so good, I think it's going to be a great relationship," Mr Trump said in the meeting in Buenos Aires on Friday local time.

"I know you've done a fantastic job in a very short period of time.

"You've done a lot of the things that they've wanted over there and that's why you're sitting right here."

Mr Morrison said Australia and the United States "have always been the greatest of friends".

"Not just in various strategic co-operation but economically, and the people-to-people relationships, well, there's none better," he said.

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The pair discussed trade, co-operation in the Pacific, and the security situations in Iran and North Korea.

The G20 started with a group photo and a warm handshake between Russian President Vladimir Putin and Saudi Arabian Crown Prince Mohammad bin Salman, who is accused of ordering the murder of journalist Jamal Khashoggi.

The summit is focused on trade, but all eyes are on Mr Trump's meeting with Chinese President Xi Jinping, which will be held on Saturday night local time.

The two superpowers have been fighting a trade war, which is threatening to hurt the global economy as billions of dollars of tariffs have been slapped on products.

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The US is also undermining the World Trade Organisation by refusing to appoint new trade judges, leading WTO boss Robert Azevedo to declare global trade is in its worst crisis since 1947.

The European Union has proposed changes to the WTO in a bid to appease the US, but so far no resolution has been found.

Mr Morrison also met with French President Emmanuel Macron to discuss the navy submarine contract, reforming the WTO and co-operation in the Indo-Pacific.

The G20 includes Argentina, Australia, Brazil, Canada, China, Germany, France, India, Indonesia, Italy, Japan, Mexico, Russia, Saudi Arabia, South Africa, South Korea, Turkey, United Kingdom, United States and the European Union.