Party chair Debbie Wasserman Schultz brought down the gavel to officially commence proceedings, launching three days of speeches by party grandees and rising stars that will culminate with Obama's acceptance speech on Thursday.

"During our national convention we will clearly demonstrate why we need to keep Barack Obama and Joe Biden in the White House!" she said.

"But this convention is about more than re-nominating President Obama. It's about Americans coming together to build one economy -- not from the top down, but from the middle class out and the bottom up.

"This convention's success will be based on engaging the American spirit and involving people who want to put their shoulders to the wheel and change our country for the better."

A group of young children performed the pledge of allegiance before Amber Riley from hit musical TV show "Glee" belted out a stirring rendition of the national anthem that reduced at least one of the party faithful to tears.

First Lady Michelle Obama is the star speaker on Tuesday night before former Democratic president Bill Clinton addresses the gathering on Wednesday, followed by Biden and Obama on Thursday.

It is nine weeks exactly before Americans decide if the country's first black president should be re-elected or if Romney, a multi-millionaire businessman and former Massachusetts governor should get to turf him out after just one term.

National polls put the rivals neck-and-neck, but a closer inspection of swing states reveals that Romney has his work cut out, especially as the bounce he was hoping for from last week's Republican convention has failed to materialize. With stalled growth and stubbornly high unemployment in the United States, arguments over who is to blame for the flagging US economy and who has the best prescription to get the country working again are dominating the campaign.