Barack Obama has been re-elected as US President - winning crucial swing states to secure a victory over Republican challenger Mitt Romney.

The Democrat gained the 270 electoral college votes needed to win a second term in office.

Obama told ecstatic supporters the "best is yet to come" in a victory speech in his home city of Chicago.

The crowd chanted "four more years" as the President arrived on stage with wife Michelle and daughters Malia And Sasha.

He praised his family, revealing he had never loved his wife more and commending his "smart, beautiful" daughters.

Obama also congratulated opponent Romney on a "hard fought campaign" and said he would work with the former Massachusetts governor to take the country forward.

The Democrat also vowed to revive the economy but warned "progress will come in fits and starts".

Tonight, more than 200 years after a former colony won the right to determine its own destiny, the task of perfecting our union moves forward. It moves forward because of you, it moves forward because you reaffirmed the spirit that has triumphed over war and oppression, the spirit that has lifted this country from the depths of despair to the great heights of hope, the belief that while each of us will pursue our own individual dreams, we are an American family and we rise or fall together as one nation and as one people. Tonight, in this election, you, the American people, reminded us that while our road has been hard, while our journey has been long, we have picked ourselves up, we have fought our way back, and we know in our hearts that for the United States of America, the best is yet to come.

Republican Mitt Romney earlier conceded defeat and phoned the President to congratulate him on his election victory.

The former Massachusetts governor urged his supporters to pray for Obama - who now faces the task of rejuvenating America's economy.

In his five minute concession speech in Boston, Romney said he and running mate Paul Ryan had "given our all" to the presidential campaign.

I so wish that I had been able to fulfil your hopes to lead the country in a different direction but the nation chose another leader and so I join with you to earnestly pray for him and for this great nation.

ITV News Correspondent Paul Davies reports on Romney's defeat:

Obama secured a convincing victory over Romney despite earlier polls suggesting the pair were neck and neck.

Under the electoral college system - which allots votes to states according to population size - Obama secured 303 while Romney is on 206.

Florida's 29 electoral college votes have yet to be declared, with Obama holding onto a slender lead in the sunshine state.

ITV News Washington Correspondent Robert Moore reports:

The President also appears to be leading in the popular vote, according to reports.

After it became clear Obama had won the election, the President tweeted "four more years" with a picture of him hugging Michelle.

Barack Obama tweeted a picture of him hugging Michelle after securing re-election. Credit: Twitter / @BarackObama

Prime Minister David Cameron - who is currently on a tour of the Middle East - sent his congratulations to Obama.

I think he's a very successful US president and I look forward to working with him in the future. I would like to congratulate Barack Obama on his re-election. I have really enjoyed working with him over the last few years and I look forward to working with him again over the next four years. There are so many things that we need to do: we need to kick start the world economy and I want to see an EU-US trade deal. Right here in Jordan I am hearing appalling stories about what has happened inside Syria so one of the first things I want to talk to Barack about is how we must do more to try and solve this crisis. Above all, congratulations to Barack. I've enjoyed working with him, I think he's a very successful US president and I look forward to working with him in the future.

The election also saw the Democrats maintain their control over the US Senate and the Republicans keep control of the House.

Read ITV News' analysis on Obama's presidential victory: