US President Barack Obama has swept to re-election Tuesday according to US media reports, creating history again by defying the undertow of a slow economic recovery and high unemployment to beat Republican foe Mitt Romney.

This is only the second time in several decades that a Democrat has won a second term in the White House.

Crowds went wild across the country as all the major US television networks projected that Obama would win at least 275 electoral votes - enough to defeat his Republican challenger Mitt Romney.

Obama grabbed Wisconsin, Michigan, Pennsylvania and New Hampshire, dramatically shrinking the Republican's chances.

“This happened because of you. Thank you,” Obama tweeted to his 22 million followers on Twitter as a flurry of states, including Iowa, which nurtured his unlikely White House dreams suddenly tipped into his column.

With a clutch of swing states, including Florida and Virginia still to be declared, Obama already had 275 electoral votes, more than the 270 needed for the White House and looked set for a comfortable victory.

There was a sudden explosion of jubilation at Obama's Chicago victory party as the first African American president, who was elected on a wave of hope and euphoria four years ago, booked another four years in the White House.

Romney's aides had predicted that a late Romney wave would sweep Obama from office after a single term haunted by a sluggish recovery from the worst economic crisis since the 1930s Great Depression and high unemployment.

But a huge cheer rang out at Obama headquarters when television networks projected Obama would retain Pennsylvania and its 20 electoral votes, and the party grew wilder as they called Wisconsin and Michigan.

The mood at Romney headquarters in Boston however had grown subdued throughout the evening as partisans stared at their smart phones.

Disappointed Republicans were seen leaving what had been billed as a celebration of Romney's expected triumph in central Washington.

Defeats in New Hampshire, where Romney has a summer home and Wisconsin, the home of Republican vice presidential nominee Paul Ryan were especially sickening for Republicans.

Early signs were that the election, while a building triumph for Obama would do little to ease the deep polarization afflicting US politics, as Republicans racked up huge margins in safe states, though struggled in battlegrounds.

Exit polls appeared to vindicate the vision of the race offered by Obama's campaign, when top aides predicted that Obama's armies of African American, Latinos and young voters would come out in droves.

Polls also showed that though only 39 percent of people believed that the economy was improving, around half of Americans blamed President George W.

Bush for the tenuous situation, and not Obama.

The president, who made history by becoming America's first black president after a euphoric victory, carved a new precedent on Tuesday by defying the portents of a hurting economy to win a second term.

He awaited his fate in his hometown of Chicago, while Romney, a multi-millionaire former investment manager and Massachusetts governor was laying low in a hotel in Boston awaiting results.

As expected, television networks projected that Republicans would win the House of Representatives.

Democrats clung onto the Senate, and retained a seat in Missouri, where Senator Claire McCaskill fended off a challenge by Representative Todd Akin, whose remarks about rape and abortion sparked national outrage.

Both presidential candidates had earlier marked time while voters dictated their fates.

Romney appeared caught up in the emotion of seeing his name on the ballot for President of the United States and also saw an omen in a huge crowd that showed up at a multi-story parking lot to see his plane land at Pittsburgh airport.

“Intellectually I felt that we're going to win this and I've felt that for some time,” Romney told reporters on his plane.

“But emotionally, just getting off the plane and seeing those people standing there... I not only think we're going to win intellectually but I feel it as well.”While Romney penned his victory speech, Obama took part in his election day tradition of playing a game of pick-up basketball with friends, including Chicago Bulls legend Scottie Pippen, after visiting a campaign office near his Chicago home.

The president, who like a third of Americans voted before election day, congratulated Romney on “a spirited campaign” despite their frequently hot tempered exchanges.

“I know that his supporters are just as engaged and just as enthusiastic and working just as hard today. We feel confident we've got the votes to win, that it's going to depend ultimately on whether those votes turn out,” he said.

“I think anybody who's running for office would be lying if they say that there's not some butterflies before the polls come in because anything can happen,” the president added later in a radio interview.

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