Former Secretary of State Powell refers to Donald Trump as "national disgrace"

Colin Powell, Secretary of State under US president George Bush, called Donald Trump a "national disgrace" and an "international pariah" in a set of emails leaked online on Tuesday.

Reported by BuzzFeed News, the emails also show Powell accusing Republican presidential nominee Trump of embracing a racist movement after questioning Barack Obama's birth certificate.

The emails surfaced at leak website DCLeaks.com, and reveal emails Powell sent to former aides.

Powell is a prominent Republican, and the leaking of the emails will cause embarrassment for the GOP ahead of the upcoming election in which Trump hopes to defeat Democrat Hillary Clinton.

Among a host of revelations from the leak, Powell adds that Trump "appeals to the worst angels of the GOP nature and poor white folks". He also recommends not givng any public attention to the nominee as "to go on and call him an idiot just emboldens him".

Trump's odds on becoming the net US president have shortened this week as Clinton struggles with issues surrounding her health and an appparent cover-up of her pneumonia diagnosis by her camaign team

The New York tycoon's share of the polls has also increased this week, with certain polls showing him pegging back Clinton's previously strong leads in key states such as Florida and Ohio.