US President Barack Obama and Republican rival Mitt Romney engaged in a frenzied cross-country blitz of the remaining toss-up states today.

Both sides predicting victory in a race that remains too close to call.

National opinion polls showed a race for the popular vote in Tuesday's election so close that only a statistically insignificant point or two separated the two rivals.

But the majority of polls in the battleground states - especially in the Midwestern states of Iowa, Wisconsin and Ohio - showed Mr Obama with a slight advantage, giving him an easier path to the 270 electoral votes needed for victory.

The final frenzy of campaigning comes in the wake of Superstorm Sandy that devastated the US East Coast.

Mr Obama had a full schedule Sunday, with campaign stops in New Hampshire, Florida, Ohio and Colorado.

Mr Romney's campaign was projecting momentum and banking on late-breaking voters to propel him to victory in the exceedingly close race.

He began Sunday with a campaign rally in Des Moines, Iowa, and also planned stops in Ohio and Virginia.

The Republican was also cutting away briefly Sunday from the nine or so competitive states that have dominated the candidates' travel itineraries to make a late play for votes in Pennsylvania, a Democratic-leaning state.

Making his closing case to voters in Des Moines, Iowa, today he pledged, if elected, to work with Democrats to restore the American dream and bring the economy roaring back to life.

"We're Americans. We can do anything," Romney said. "The only thing that stands between us and some of the best years we can imagine is a lack of leadership - and that's why we have elections."

In the final days of his final campaign, Obama has been imploring crowds at his rallies - and the wider electorate - to let him finish what he started.

The nation has been bruised by recession and war, he contends, but remains resilient and is coming back.

Mr Obama, too, said he is willing to work across party lines to break Washington's gridlock, but assured some 14,000 supporters who gathered in Concord, New Hampshire, that he would not compromise key Democratic priorities such as health care and college financial aid.

"I know I look a little bit older, but I've got a lot of fight left in me," Mr Obama said. "We have come too far to turn back now. We have come too far to let our hearts grow faint. It's time to keep pushing forward."

Mr Obama's campaign said it had registered 1.8 million voters in key battleground states, nearly double the number of voters they registered in 2008.

Campaign officials said volunteers had made 125 million personal phone calls or door knocks with voters.