CHARLOTTE, N.C. -- Barack Obama, his re-election in doubt, promised better days ahead as he accepted the Democratic Party nomination for president before thousands of charged-up party loyalists and millions of television viewers.

In a crucial speech at the Democratic National Convention, just two months before the Nov. 6 vote, Obama looked to reignite the excitement that powered his first run for the presidency. Obama needed to win over undecided voters, especially those who had been swayed by his inspiring message of hope in 2008, but now feel disillusioned after years of economic weakness and persistent political bickering.

He assured them: "Our problems can be solved, our challenges can be met."

"Yes, our path is harder -- but it leads to a better place," he said.

Obama built on the message delivered throughout the convention: that America is on the road to recovery while Republican rival Mitt Romney would revive failed policies, cutting taxes for the rich and slashing programs that give regular Americans a chance for a more prosperous future.

Republicans, who nominated Romney last week, argue that America's high 8.3 per cent unemployment rate is proof that Obama's policies have failed and that the president's spendthrift, big-government policies have hurt business and caused the federal deficit to soar.

The two candidates are locked in tight race. Polls show that Romney, a wealthy businessman and former governor of Massachusetts, is seen as the better candidate for improving the economy, while Obama is viewed as more likable and having a better understanding of everyday Americans.

Obama's speech marked the climax of the three-day convention. First lady Michelle Obama highlighted the first day, talking about her husband's humble roots and compassion for those living through tough times. Bill Clinton, the popular former president who led the United States during years of prosperity, gave a rousing speech Wednesday, vouching for Obama's economic policies and urging Americans not to turn back to Republicans. After Clinton's speech, Democrats formally approved Obama's nomination in a rollcall vote.

Among the speakers preceding Obama on Thursday were actress Eva Longoria and Vice-President Joe Biden, who was formally re-nominated. "We're on a mission to move this nation forward -- from doubt and downturn to promise and prosperity," Biden said in his acceptance speech.

Obama needed to strike a balance in his speech, highlighting improvement in the economy without suggesting that things are fine as they are. Democrats argue that the economy would be worse if it hadn't been for Obama-led programs to rescue the auto industry and stimulate the economy. Still, it is difficult to win over voters by arguing that things could have been worse.

Obama was setting out a goal of creating 1 million new manufacturing jobs by the end of 2016 and push for more aggressive steps to reduce American dependence on foreign oil.

Still, he said, "The truth is it will take more than a few years for us to solve challenges that have built up over a decade."

Obama's biggest domestic achievement was passage of a health care overhaul, yet Democrats discuss that with some caution because polls show most Americans oppose his plan.

The economy has dominated the presidential campaign, but Democrats are also highlighting national security issues, where Obama does well in polls. They praised Obama for fulfilling his promise to end U.S. combat operations in Iraq and for his order that led to the killing of terrorist leader Osama bin Laden.

Mocking a Republican slogan asking Americans if they are better off under Obama, John Kerry, the Democratic presidential nominee in 2004, told delegates: "Ask Osama bin Laden if he's better off now than he was four years ago."

Yet Obama has not followed through on other commitments from 2008: He has not closed the U.S. prison for terrorists in Guantanamo Bay, Cuba, and he failed to win approval for legislation fighting climate change.

In addition to winning over undecided voters, Obama will try to fire up the Democratic base and fatten his campaign coffers. Romney and Republicans have a strong lead in fundraising, a striking reversal from 2008 when Obama held an overwhelming advantage over then-rival John McCain. Independent groups seeking Romney's election are pouring tens of millions of dollars into television advertising, far exceeding what Obama's supporters can afford.

Citing a chance of thunderstorms, convention organizers scrapped plans for Obama to speak to an enormous crowd in a 74,000-seat outdoor stadium and decided to shoehorn the event into the convention arena, which accommodates 15,000.

That meant a far smaller crowd than the president's campaign hoped would hear him speak and present an enthusiastic show of support on television

Romney was wrapping up several days of rehearsals ahead of an Oct. 3 debate with Obama, the first of three. He is expected to resume full-time campaigning within days.

Romney said he had no plans to watch Obama on television.

"If the president is going to report on the promises he made and how he has performed in those promises, I'd love to watch it," Romney said. "But if it's another series of new promises that he's not going to keep, I have no interest in seeing him because I saw the promises last time."