President Barack Obama has delivered an impassioned plea for voters to turn out for Hillary Clinton, warning that not just his legacy but also the country is at risk if Donald Trump becomes president.

Obama told voters in the crucial swing state North Carolina - which he lost in 2012 - that the future of the country rested in their hands as he launched a blistering attack on Trump, describing him as "uniquely unqualified" to be commander-in-chief.

"I ran against John McCain, I ran against Mitt Romney - I thought I would be a better president but I never thought that the Republic was at risk if they were elected," Obama warned.

He urged the large crowd to look past "the noise" of the ugly election campaign and to elect Clinton as the first female president.

"Choose hope! Choose hope! Choose hope! Vote and if you do, we will elect Hillary Clinton as the next president of the United States."