US President Barack Obama has beaten his Republican challenger Mitt Romney to win a second term at the White House, TV networks projected Tuesday.

In a tweet to supporters, Obama wrote "This happened because of you. Thank you," as crowds cheered in Chicago headquarters, waiting for him to come out and address the nation.

Obama was projected to have won several key swing states, including Ohio, Pennsylvania, Wisconsin, Iowa, Nevada and New Hampshire, while Romney only won North Carolina. Florida and Virginia remained too close to call.

The relentless battle for the swing states gave Obama at least 290 electoral votes, while Romney just got 201 shortly after midnight.

Obama easily grabbed a host of "deep blue" states including California, Illinois and New Jersey, while Romney prevailed in "deep red" states of Texas, Kentucky and Georgia.

While Obama supporters have already started celebrations of his reelection, Obama himself has yet to make a victory speech while Romney has not conceded defeat either.

Meanwhile, Obama's Democratic Party is also projected by CNN to retain control of the Senate while Fox News projected that the Republican Party will hold onto control of the House of Representatives.

In addition to the massive task of tackling 1 trillion-dollar annual deficits and reducing a 16 trillion-dollar national debt, Obama will have to deal with a divided US Congress that is likely to maintain the same partisan makeup in his second term in the White House.

The Election Day began with midnight voting in a pair of small towns in New Hampshire, and expanded across the nation after 5 a.m. (1000 GMT).Voters lined up from New York to Florida to cast their ballots.

Although final figures haven't come in, US media outlets are reporting heavy turnout in the election. Early exit polls showed 73 percent of voters were white, 13 percent were African American, 10 percent Latino and 3 percent Asian.

In preliminary results from early voters in the national NBC News exit poll, 52 percent said America was on the wrong track while 46 percent said the nation was "generally going in the right direction."

Not surprisingly three out of five voters Tuesday said the economy was the most important issue facing the country, but poll respondents were divided as to what specific economic challenge loomed largest.

In picking the biggest economic problem facing people like yourself, 39 percent chose unemployment, 36 percent said rising prices, while 14 percent said taxes were the biggest problem and 7 percent said housing.