However, the prime minister does say it appears Mr Trump has "tremendous support" among Americans.

The two leaders spoke on stage together against a giant backdrop of the US and Australian flags at the opening of billionaire box-maker Anthony Pratt's newest paper recycling factory in Ohio on Sunday.

The event had the flavour of a campaign rally, with nearly 2000 people clad in Trump T-shirts and caps bearing his "Make America great again" slogan cheering every few sentences.

And people lined the road through Wapakoneta, where the factory is located, to wave Trump flags and even salute when the motorcades drove past.

"We love jobs!" Mr Trump told the crowd.

And Mr Morrison contributed: "We're making jobs great again!"

The president praised Mr Morrison, saying of the recent federal election: "It was supposed to be close and he blew them away because he believes a lot of the same things I believe."

Asked whether he'd return the endorsement, Mr Morrison said it wasn't the job of a foreign prime minister to involve themselves in domestic American politics.

"But as you can see, we do share a lot of the same views," he told reporters in Chicago on Monday.

"He clearly has tremendous support for that.

"And I think you could see that on display as we made our way to the Pratt plant."

Mr Trump faces a re-election fight in November 2020 but the nature of the American system means he has already started campaigning as his Democratic opponents duke it out to become their party's candidate.

Australian Associated Press