WASHINGTON (AFP) - Former US secretary of state Colin Powell dubbed Donald Trump a "national disgrace" and an "international pariah" in personal e-mail exchanges hacked and leaked online.

The leaked correspondence reveals a stinging indictment of the brash billionaire by a Cabinet member in the last Republican president's administration, albeit one who twice endorsed Barack Obama for president.

"He appeals to the worst angels of the GOP nature and poor white folks," Powell wrote of the Republican White House nominee, in one of the messages obtained by DC Leaks, a website affiliated with other recent hacks of high-profile US figures, and first published by Buzzfeed.

In an exchange last month with a former aide, Powell blasts the so-called "birther" movement that sought to question Obama's American nationality - and was spearheaded by Trump - as "racist".

"Yup, the whole birther movement was racist," wrote the retired general. "That's what the 99% believe. When Trump couldn't keep that up he said he also wanted to see if the certificate noted that he was a Muslim."

Powell, who was secretary of state from 2001 to 2005, confirmed to NBC that the leaked messages were authentic, and said the hackers were in possession of "a lot more."

According to The Daily Caller, hackers are thought to have provided DC Leaks with some 30,000 of Powell's e-mails.

Powell made headlines recently when it emerged that he had counselled Hillary Clinton on how best to keep official e-mails out of public view, when she took office at the State Department.

The now-closed FBI investigation into the Democrat's use of a private e-mail server has dogged her White House campaign.

In a leaked e-mail exchange reported by NBC, Powell voiced frustration about his name being linked to the e-mail uproar.

"I have told Hillary's minions repeatedly that they are making a mistake trying to drag me in, yet they still try," Powell wrote in August.