President Barack Obama won re-election to a second term in the White House on Tuesday, television networks projected, beating Republican challenger Mitt Romney after a long and bitter campaign.

Obama defeated Romney in a series of key swing states despite a weak economic recovery and persistent high unemployment as voters decided between two starkly different visions for the country.

Obama's victory in the hotly contested swing state of Ohio - as projected by TV networks - put him over the top in the fight for the 270 electoral votes needed to clinch the White House and ended Romney's hopes of pulling off a string of swing-state upsets.

Obama scored narrow wins in Ohio, Wisconsin, Iowa, Pennsylvania and New Hampshire - all states that Romney had contested - while the only swing state captured by Romney was North Carolina, according to network projections.

CBS projected that Obama won the swing state of Nevada in Tuesday's presidential election. Obama won the state, which has six electoral votes, in 2008 as well.

► NH presidential voting results

At least 120 million American voters had been expected to cast votes in the race between the Democratic incumbent and Romney after a campaign focused on how to repair the ailing economy.

Obama enters his second four-year term faced with a difficult task of tackling $1 trillion annual deficits, reducing a $16 trillion national debt, overhauling expensive social programs and dealing with a gridlocked Congress that looked likely to maintain the same partisan makeup.

Each man offered different policies to cure what ails America's weak economy, with Obama pledging to raise taxes on the wealthy and Romney offering across-the-board tax cuts as a way to ignite strong economic growth.

Inside Obama's Chicago campaign headquarters, staffers erupted into cheers and high-fives as state after state was called for the president.

Obama watched the returns on television at his Chicago home. Senior campaign strategist David Axelrod said via email that he was feeling "great."

Romney made last-minute visits to Ohio and Pennsylvania on Tuesday to try to drive up turnout in those states, while Vice President Joe Biden was dispatched to Ohio. Obama remained in his hometown of Chicago.