Washington: Donald Trump has unleashed a series of nasty personal attacks against his Democratic opponent, Hillary Clinton, mocking her appearance and questioning her mental health several times during a campaign rally and on social media.

"She is a totally unhinged person. She's unbalanced. And all you have to do is watch her, see her, read about her," Trump said during a campaign rally in Windham, New Hampshire, on Saturday evening.

"She will cause - if she wins, which hopefully she won't - the destruction of our country from within."

The Republican presidential nominee called Clinton unstable and incompetent several times throughout the rally. At one point, he also called her "Hillary Rotten Clinton", a play on her maiden name, Rodham.