WASHINGTON, D.C.: US President Barack Obama swept to an emphatic re-election win over Republican rival Mitt Romney on Tuesday, making history by transcending a dragging economy and the stifling unemployment that haunted his first term.

The 44th US president and the first African American to claim the Oval Office was returned to power after a joyless election, which appears to have deepened, rather than healed, his nation's political divides.

"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," Obama, 51, said at a victory party in Chicago.

"I have never been more hopeful about America. And I ask you to sustain that hope," Obama said, striving for inspiration rarely shown in a campaign where the prophet of hope of 2008 became a conventional, brawling politician.

"I have always believed that hope is that stubborn thing inside us that insists, despite all the evidence to the contrary, that something better awaits us so long as we have the courage to keep reaching, to keep working, to keep fighting."

With only Florida among the battleground states still to be declared, Obama had 303 electoral votes, well over the 270 needed to win the White House.

He had a slim lead in the national popular vote, leading Romney by 50 percent to 49 percent, after drawing more than 56 million votes. Turnout appeared strong, though official figures had yet to be released.

As Obama's victory was confirmed with wins in rustbelt Ohio and his spiritual political home in Iowa, large crowds suddenly materialized outside the White House, chanting "four more years" and "O-bama, O-bama."

Republican nominee Romney, 65, deflated and exhausted, offered a classy tribute, as he consoled dejected supporters in Boston moments after phoning Obama to formally concede.

"This is a time of great challenges for America and I pray that the president will be successful in guiding our nation." Romney said.

In a show of bipartisanship after a searing campaign, the president said that he wanted to meet his vanquished foe to find common ground to move America forward.

Obama's victory means that he will get the chance to embed his healthcare and Wall Street reforms deep into the fabric of American life—Romney had pledged one of his first acts would be the repeal of Obamacare.

He may also get the chance to reshape the Supreme Court in his liberal image for a generation, a move that would shape policy on issues like abortion and gay rights.

The president will also look abroad as he builds his legacy, and will face an immediate challenge early in 2013 over whether to use military force to thwart Iran's nuclear program.

Obama's win on Tuesday bucked history, as it came with the unemployment rate pegged at 7.9 percent, the highest level for a re-elected president in more than 70 years.

Remarkably, his coalition of Hispanic, black, and young voters turned out in similar numbers to those of his heady change-fueled campaign in 2008, shocking Romney's team and presenting a new American face to the world.

But once the euphoria fades, the president will face a tough task enacting his second term agenda after Republicans, who thwarted him repeatedly in his first mandate, retained control of the House of Representatives.

Democrats kept the Senate but fell short of the 60-vote super majority needed to sidestep Republican blocking tactics.

The president paved the way to victory with a staunch defense of Democratic bastions in Pennsylvania, Wisconsin and Michigan, at which Romney had taken a last-minute run when he saw more conventional paths to the White House blocked.

Obama also locked in swing states, including Virginia—where he became the first Democrat to win since 1964 four years ago—Nevada, Ohio, New Hampshire, Colorado and Iowa, crushing Romney's slim hopes of a viable path to victory.

Romney could only wrestle Indiana and North Carolina from Obama's 2008 map.

The win in Iowa will be especially sweet for Obama, as the heartland state nurtured his unlikely White House dreams way back in 2007. A tear rolled down his cheek as he held his last-ever campaign rally there on Monday.

His victory in Ohio represents a delayed repayment for his gutsy call in 2009 to mandate a federal bailout of the auto industry, on which one in eight jobs in the state depend. Romney had opposed the move.

Obama won with a fiercely negative campaign branding Romney—a multi-millionaire former corporate turnaround wizard—as indifferent to the woes of the middle class.

World leaders on Wednesday hailed President Barack Obama's sweeping re-election, with allies pledging to deepen cooperation with the United States on fighting the world economic slump and maintaining security across the globe.

Congratulations poured in from across the world, including fellow UN Security Council members Britain, China, France and Russia as well as its staunch Middle East ally Israel and Obama's ancestral home in Kenya.

Russia President Vladimir Putin, whose relations with Washington have often been frosty, sent a telegram congratulating Obama on his victory over Republican challenger Mitt Romney.

"We hope that the positive beginnings that have taken hold in Russian-US relations on the world arena will grow in the interests of international security and stability," Russian news agencies quoted Putin's spokesman Dmitry Peskov as saying.

Moscow is ready to "go as far as the US administration is willing to go," Foreign Minister Sergei Lavrov was quoted as saying by the RIA Novosti news agency.

In Beijing, Chinese President Hu Jintao, who himself is handing over power at a Communist Party congress starting this week, noted "positive progress" in Sino-US relations over the past four years despite tensions over issues such as trade and territorial disputes involving US allies.

China will "look to the future and make continuous efforts for fresh and greater progress in the building of the China-US cooperative partnership," Foreign ministry spokesman Hong Lei told reporters.

Israeli Prime Minister Benjamin Netanyahu, who at times appeared to have tense relations with Obama, also joined the well-wishers.

"I will continue to work with President Obama to ensure the vital security interests of Israel and the United States," said Netanyahu, who had appeared to throw his support behind Romney during the election campaign.

Iran, facing Western pressure particularly from the United States as well as archfoe Israel over its controversial nuclear drive, has yet to comment on Obama's win.

British Prime Minister David Cameron said that he was looking forward to working again with his "friend" Obama on several fronts, including kickstarting the world economy and finding a solution for the escalating Syria conflict.

"There are so many things that we need to do: we need to kickstart the world economy and I want to see an EU-US trade deal," Cameron said.