Hillary Clinton will be competing in the 2016 race for the White House in a bid to become the first female US president.

The former US Secretary of State made the announcement on her website on 12 April several minutes after emails from her campaign chairman, John D. Podesta, confirmed: "It's official, Hillary's running for president."

Launching her campaign website, Hillary told Americans she wanted to be their "champion" in a video where she appears at the end and says: "The deck is still stacked in favor of those at the top.

"Everyday Americans need a champion, and I want to be that champion. So I'm hitting the road to earn your vote — because it's your time. And I hope you'll join me on this journey."

Podesta said Hillary will host a formal kickoff event next month and will soon meet voters in Iowa and New Hampshire.

Hillary's campaign manager, Robby Mook, 35, has already sent field organizers to Iowa, New Hampshire, Nevada and South Carolina.

The central theme of her candidacy is to improve the economic conditions of the middle class, improving wages and decreasing income inequalities.

Hillary, 67, previously ran for the Democratic presidential nomination in 2008, but lost to present US President Barack Obama.

Her candidacy has been predicted for months now in what is being termed as one of the least contested races for the Democratic presidential nomination in comparison to 2008 when Hillary faced tough rival, Barack Obama.

An estimated 81 per cent of Democrats have said they would consider voting for her, according to a CBS News poll.

"Being the first woman to run for president with a real chance of winning, that's a wild card, but potentially a net positive, particularly for undecided women," said Scott Keeter, director of survey research at the Pew Research Center, reported The New York Times.

Meanwhile, Obama said Hillary would make "an excellent president".

"She was a formidable candidate in 2008. She was a great supporter of mine in the general election. She was an outstanding secretary of state. She is my friend," said Obama, as quoted by the Daily Mail.