There was a sudden explosion of jubilation at Obama’s campaign headquarters in Chicago. President Obama tweeted a photograph of himself hugging his wife Michelle with the caption “four more years”.

Meanwhile, Republican candidate Mitt Romney has conceded defeat in the race for the White House, saying: “I have just called President Obama to congratulate him on his victory.”

Obama defeated Romney in a series of key swing states despite a weak financial recovery and high unemployment.

The president, who made history by becoming America’s first black president in 2008 has captured at least 275 electoral votes – more than the majority of 270 required for victory in Tuesday’s quadrennial election while Romney captured 203 according to CNN.

Obama won a string of battleground states, including Ohio, Pennsylvania, Wisconsin, Iowa and New Hampshire, meaning that the win was all but guaranteed, though the vote-counting was far from complete.

Romney has taken 203 electoral votes from 23 states, including Texas, Louisiana, Kentucky, Indiana, South Carolina, Georgia, Oklahoma, Tennessee, Utah and Alabama, according to Washington Post.

As soon as the results were announced by news networks, Obama posted on his official account on Twitter: “This happened because of you. Thank you,” signed with his initials “bo” to mark it as a personal message.

At least 120 million American voters were expected to cast votes in the race between the Democratic Obama and Romney after a campaign which mainly focused on how to repair the ailing U.S. economy.

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

Democrats also held onto their majority in the Senate, picking up two seats in early returns with the possibility of a third.