Donald Trump's son, Donald Trump Jr, had some reassuring words for voters before the first presidential debate with Hillary Clinton.

While the Democratic campaign has sought to portray Trump as a loose cannon and a threat to global security, the opposite is actually the case, according to Trump Jr.

"For those who say: 'Oh he's so dangerous', there is nothing dangerous about it," he told Sky News.

"My father's going to have the media, everyone, both sides – Republican, Democrats – watching every move that he makes.

"He is going to have the greatest system of checks and balances in place watching him."

Trump Jr made the comments in response to a question about the appeal of his father's message to undecided and independent voters.

"If Hillary Clinton gets in, the media is going to give her a pass as they have with every scandal she's had for the last 30 years, everything that's going to go unchecked," he said.

"The liberals will push that agenda and the Republicans have shown that they're, generally speaking, too weak to actually take them on.

"So the safe candidate is the guy who is going to have the scrutiny of the world watching him and I think that should go a long way with people who are undecided, who may not be thrilled with the other choice.

"We're way ahead with undecided voters, independents and all those guys who don't have a party allegiance. We're doing well with them."

Donald Trump Jr has found himself under intense scrutiny in the run-up to the presidential debate, after tweeting an image comparing refugees to poisoned Skittles.

Donald Trump and Donald Trump Jr
Donald Trump and Donald Trump Jr REUTERS/Aaron Josefczyk