Democratic presidential nominee is the only candidate in the race to the White House who has devoted her entire life to the people of America, outgoing US President Barack Obama has said.

"There's only one candidate in this race who has devoted her entire life to lifting up that better America - and that is next President of the United States, Hillary Rodham Clinton. She's the right person. She's the right person at the right time," Obama, 55, said at an election rally in Raleigh, North Carolina yesterday.

He said Clinton's opponent was someone whom his own party leaders in the past had declared a con artist.

"This choice actually is pretty clear, because the guy that the Republicans nominated - even though a bunch of them knew they shouldn't nominate him - the guy they nominated who many of the Republicans he is running against said was a con-artist and a know-nothing and wasn't qualified to hold this office," Obama alleged.

"This guy is temperamentally unfit to be Commander in Chief and he is not equipped to be President. This should not be a controversial claim. It really shouldn't. It's strange how, over time, what is crazy gets normalised and we just kind of assume, well, you know what, he said a hundred crazy things, so the hundred-and-first thing we just don't even notice," he said.

Obama said the US could not afford a President who suggests that America should torture people or that it should ban entire religions from the country.

"We deserve better than a Commander-in-Chief who insults POWs, or attacks a Gold Star mom, or denigrates our troops. This is somebody who vilifies minorities, vilifies immigrants, vilifies people of Muslim faith, makes fun of Americans with disabilities," he said.

How is that person going to be your voice? Do you want somebody to be your voice who on tape brags about how being famous allows him to get away with sexual assault? Who calls women 'pigs', or 'dogs', or 'slobs' and grades them on a scale of one to ten? That is not the voice of America, Obama asked and the audience responded with a big "No".

"We have a choice. We can choose to teach our kids that our diversity is our strength; that women are full and equal citizens capable of doing anything a man does - that our job, particularly when we have positions of authority, particularly when this country has blessed us, is to treat everybody with dignity, treat everybody with respect, to treat everybody with generosity and kindness," he said.

"We have to stop thinking that his behaviour is normal, that it's within the bound of what has, up until this point, been our normal political discourse. You hear some folks now justifying it and making excuses," he said.

Obama made a strong case for Clinton as the next president

of the United States.

"Hillary hasn't stopped fighting for justice, hasn't stopped fighting for equality ever since. Her heart has always been in the right place, and she works hard every single day. First of all, she ran against me, and she worked really hard. And then she worked for me, and she worked really hard," he said.

"She was there in the Situation Room, and she was there in the Oval Office. When we were making big decisions about going after bin Laden even when it was risky, when it was time for us to figure out how to win back world opinion in the wake of the Iraq war, she circled the globe tirelessly as Secretary of State, earned the respect of world leaders," he added.

Clinton is not flashy, he observed.

Noting that sometimes Clinton is "underappreciated" here at home, Obama said she made me a better President and is an outstanding public servant who knows her stuff.

"She understands the challenges we face. She is tough. When things don't go her way, she doesn't whine, and she doesn't complain. She doesn't blame others, suggesting everything is rigged," he said in an apparent reference to the recent statements of Trump.

Clinton works through whatever is in front of her. She has got grit and she has got resilience, Obama said.

"If she gets knocked down, she just comes back up and she goes back at it. And she knows, most importantly, what the decisions that a President makes means to you," Obama said.

He said Clinton will be a Commander-in-Chief who finishes the job defeating ISIS.

"She will be smart and she will be steady," he said.