WASHINGTON - Hillary Clinton cast herself as a champion for everyday Americans on Sunday, kicking off her long-awaited second run for the White House with a vow to fight for a level playing field for those recovering from tough economic times.

Her campaign kick-off video features two same-sex couples - one of them getting married in summer- a new retiree and a college student searching for a job. It also stars a young mother who's moving so her daughter can attend a better kindergarten, Spanish-speaking brothers opening a new business and an African-American couple preparing for the birth of their first child, AFP reported.

The slickly produced video quickly went viral after it was posted on Clinton's revamped campaign website on Sunday.

"I'm getting ready to do something, too. I'm running for president," says Clinton.

"Americans have fought their way back from tough economic times, but the deck is still stacked in favour of those at the top.

"Everyday Americans need a champion, and I want to be that champion - so you can do more than just get by - you can get ahead. And stay ahead. Because when families are strong, America is strong.

"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."

The vibrant clip, set to snappy music and featuring Clinton for less than half the video's length, is a dramatic departure from her drab announcement of seven years ago, according to AFP.

That video, which kicked off her former unsuccessful campaign, showed Clinton on a couch, talking about ending the Iraq war, shrinking deficits and expanding affordable health care. It made no mention of same-sex unions.

During her campaign, Clinton plans to highlight that she is a grandmother and trumpet her chance to make history, New York Times said.

"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 Centre.

One of the same-sex couple in the video, Jared Milrad and Nate Johnson, had participated in a video about "big changes" and had no idea that their wedding plans would feature in Clinton's campaign launch.

Friends called to say they saw the pair walking hand in hand in what quickly became one of the most widely viewed political clips of the year.

"We were both out shopping, working on wedding invitations," Milrad told AFP, overjoyed to be part of the Clinton rollout - and part of a large-scale change in US social attitudes.

"It shows how far we've come," said the 31-year-old lawyer, pleased that public support for same-sex marriage rights has grown so far as to appear in a presidential campaign launch.

Reactions were mixed to Clinton's campaign, with one New York Times online reader Caitlin saying: "I am a 24 year old, multi-racial, self-supporting college graduate with two jobs living in Brooklyn - a quintessential millennial, if you will. My peers and I are overwhelmingly enthusiastic about Hillary's announcement. She is an inspiring and profoundly qualified leader who consistently champions the causes that are on the right side of history."

"Awesome video! Go girl!!! You've got this,'' Lisa Kunze wrote on Clinton's Facebook page.

"So proud of you Hillary! Supported you and saw you in 2008, more than ever I support you now. I got my bumper sticker at least a year ago. Let's win this! Patty Melt said.

Tony Marcelonis was among those who felt that Clinton was not the right presidential candidate. "I am all for a women president...just not that women. Is it more important to make history or bring this country back to the people," he wrote on Facebook.

David Paulus said: "I'm a life long Democrat but Hillary needs to retire, The country needs something better than a re-hashing of the past."