Shorten fears Trump would be 'difficult'

Opposition Leader Bill Shorten is making no apologies for blasting Donald Trump and his "extreme views".

Mr Shorten says the presumptive Republican presidential nominee would be "very difficult" to deal with.

"I don't resile from standing up for Australia," he told reporters in Adelaide on Tuesday.

"I think there are a lot of people who want to see Australia's political leaders not sit on the fence but actually state what they think."

Mr Shorten is openly endorsing Democrat Hillary Clinton who he says would make a better president.

He believes he has the backing of many people concerned with some of Mr Trump's "extreme views".

Nevertheless, Mr Shorten says Australia's alliance with the US will continue to remain strong even under Mr Trump.

"Whoever the Americans elect we will work with."