Hillary Clinton has branded fellow Presidential hopeful Donald Trump "temperamentally unfit" to hold the office of President of the United States.

Speaking at an event in San Diego the former First Lady stated her opponent's ideas were "dangerously incoherent" and he "should not have the nuclear codes" as she believed he was unprepared for the responsibility.

Trump quickly hit back by responding to Clinton's criticism by tweeting "She doesn't even look presidential!"

The criticism of Trump came just one day after Clinton branded the Republican candidate a "fraud".