5.45pm: PRESIDENT Barack Obama has promised Americans "the best is yet to come" after he secured a second term in the White House on Wednesday (AEDST).
Mr Obama won almost all of the key swing states as he saw off Republican challenger Mitt Romney.
Using the popular vote as a measure, the election was as close as everyone had predicted.
In fact, Mr Romney was leading the popular vote for much of the count, before being overtaken late by Mr Obama.
But US elections are not decided on the popular vote.
As of writing, Mr Obama had secured at least 303 electoral college votes - each state carries a certain number - easily eclipsing the 270 needed for victory, but a long way short of the 365 he secured in his landslide victory in 2008. Mr Romney had 206.
While Mr Romney carried the battleground states of North Carolina and Indiana, the remainder had either gone, or looked like going to the president.
Put simply, Mr Obama prevailed in the states that counted.
There were no "yes we can" moments of four years ago, but Mr Obama's 20-minute victory speech was one for the ages.
In essence, it was designed to begin the process of uniting a divided nation.
Mr Obama conceded it would take more than words to heal the rift.
But it was a start.
And whereas in 2008 he was solemn and appeared overwhelmed by the enormity of the task at hand, Mr Obama was exuberant in accepting victory this time around.
For a country that has been battered by the global financial crisis, chronic unemployment, wars in two countries and savage partisan politics, his was a message of hope.
"I've never been more hopeful about our future ... about America," Mr Obama said in his home town of Chicago.
"I believe we can seize this future together. Because we are not as divided as our politics suggest. We're not as cynical as the pundits believe. We are greater than the sum of our individual ambitions and we remain more than a collection of red states and blue states.
"We are, and forever will be, the United States of America."
Mr Obama used much of the speech to focus on the American people. He thanked Democrats and Republicans for taking part in the election and called on all Americans to play their part in lifting the country off the mat.
And he said he would continue to draw inspiration from their strength and resilience.
"You've made me a better president. And with your stories, and your struggles, I return to the White House more determined and more inspired than ever," he said.
"Tonight you voted for action, not politics as usual."
Mr Romney was gracious in defeat, calling for both sides of politics to work together for the good of the country.
"The nation ... is at a critical point. At a time like this we can't risk partisan bickering and political posturing," Mr Romney told the Republican faithful.
"Our leaders have to reach across the aisle to do the people's work."
He congratulated Mr Obama and said he would pray the "president will be successful in guiding our nation".
Australian Prime Minister Julia Gillard also used Twitter to congratulate Mr Obama.
"My sincere congratulations to President @BarackObama on your re-election! JG."
She then issued a statement saying she was looking forward to continuing working with the president.
"Australia has worked closely with President Obama and his administration over the past four years.
" I look forward to continuing this friendship," Ms Gillard said.
Opposition Leader Tony Abbott also offered his congratulations.
"It was a hard-fought contest worthy of one of the world's greatest democracies," Mr Abbott said.
News of Mr Obama's re-election sparked a frenzy of activity on Twitter, with the social network site reporting 327,000 tweets per minute being sent.
A photo of Mr Obama hugging his wife Michelle with the words "four more years" had been retweeted almost 400,000 times.
Earlier, Mr Obama tweeted this to his more than 22 million followers: "We're all in this together. That's how we campaigned, and that's who we are. Thank you. -bo."
Mr Obama will not have the pressure of campaigning for re-election in four years, but he will still have to battle a hostile House of Representative to get legislation through Congress.
Wednesday's election did little to change the make-up of Congress. The Republicans will continue to enjoy a comfortable majority in the House, while the Democrats' control of the Senate will remain intact.
2:20pm: Barack Obama has won the 2012 Presidential election, with CNN, MSNBC and Fox all projecting that he has been re-elected.
While the most important trio of battlegrounds - Ohio, Florida and Virginia - remain too close to call, Obama has grabbed Wisconsin, Michigan, Pennsylvania and New Hampshire, dramatically shrinking the Republican's chances.
US news network voting projections had Romney leading Obama by 184 to 173 electoral college votes, but the Democratic incumbent appeared to have a far clearer route to victory ahead of him.
As expected, Obama polled strongly in New England and the industrial northeast, grabbing densely populated states like New York, New Jersey and Wisconsin, according to news network projections.
His rival Romney did predictably well in the southern Bible Belt and western prairie states, winning the major prize of Texas and taking back Indiana, which Obama won in 2008.
But Romney failed to win Michigan, his home state where his father served as governor, and the key battleground states of Florida, Virginia, North Carolina and Ohio remained too close to call.
Obama also won New Hampshire, which had been considered a swing state, and Wisconsin, the home state of Romney's running mate Paul Ryan.
UPDATE: President Barack Obama has taken two big strides towards re-election by blocking Mitt Romney's grab for Pennsylvania and Wisconsin, the first key states called in their bitter White House race.
Romney had made a late run at the solidly Democratic states, as his aides predicted a late wave would oust Obama, 51, from the Oval Office after one term as he struggled to deal with a slow economic recovery and high unemployment.
A huge cheer rang out at Obama headquarters when television networks projected Obama would retain Pennsylvania and its 20 electoral votes.
Obama's Midwestern line of defence also appeared to be holding, as networks called Wisconsin, the first of a trio of Obama firewall states, also including Iowa and Ohio, in a blow to native son Paul Ryan, the Republican vice presidential nominee.
In another blow to Romney, Obama also captured the northeastern swing state of New Hampshire, which was de-facto home ground for the Republican as he has a holiday home there, and was governor of neighbouring Massachusetts.
Early in what was expected to be a long evening of vote-counting, Obama had 158 and Romney had 154 of the 270 votes needed in the state-by-state electoral college needed to claim the White House.
The results so far declared left Obama with a much easier path to the White House than his rival and Romney appeared to need at least five of the remaining seven swing states, possibly including Florida, Ohio, and Virginia.
EARLIER: President Barack Obama danced on the stage wrapping up a rally in Cincinnati, Ohio, on Saturday night.
Monday - his last ever rally as an election candidate - he bounded forth with a wide grin before an overflow crowd in Madison, Wisconsin, energised by ballads from Bruce Springsteen.
Did the whiff of victory - hard-fought for sure - hang here in the cold, blue-sky air?
The fate and the legacy of Mr Obama, the bruised Messiah for hope and change, are in the hands now not of himself, his advertising gurus or campaign advisers but of the American people who will pour into polling stations today.
Complacency remains a luxury unavailable to him; yet the runes seem clear, something is nudging his way.
For one more gruelling day of hop-scotch rallies across four swing states the task for Mr Obama was to cajole his supporters to turn out and to detail the case for himself and against Mitt Romney.
"Our work is not yet done," he declared here, saying the nation faced a historic choice between two distinct visions.
"It's a choice between returning to the top-down policies that crashed our economy or a future that provides opportunities for everybody."
Some national polls still show a tie with his Republican foe.
The final national NBC/Wall Street Journal survey has Mr Obama with the support of 48 per cent of likely voters and Mr Romney securing 47 per cent.
But the polls that mattered - here in Wisconsin and the other eight battleground states - told the more compelling story; that the avenues to the 270 Electoral College votes needed to win looked more numerous and more wide for the incumbent.
Crucially, it would seem Mr Obama has held on to his edge, or even built on it, in the Midwest, notably in Ohio, but also here in Wisconsin and Iowa.
Already, moreover, he has built an advantage in early voting patterns.
Upwards of 30 million Americans had already voted in 34 states and the District of Columbia by last night.
Those early votes have established leads for the President in Nevada, Iowa and Ohio, even if not by the margins of 2008.
"Here's what I predict, it will not be tied tomorrow," David Axelrod, the Obama strategist, boldly told a huddle of reporters, asserting that "all those pathways" to a College victory he had laid out one year ago, "are intact".
"We feel good here in Wisconsin where we have a solid lead and have the enthusiasm.
"We are going to have a good day in Ohio and we are going to have a good day in Iowa."
In Florida, President Obama is "competitive", he said only.
Pundits are naturally shy of iron-clad predictions.
Those reporters who were in Crawford, Texas, in 2004 remember a downcast George W Bush registering his vote with models showing a very slim lead that election day for the Democrat, John Kerry.
The evangelical surge changed all that and Mr Bush instead won a second term. But still. The Associated Press offered its own final analysis.
Mr Obama was almost assured 249 Electoral College votes by carrying 20 states that are reliably Democratic or leaning his way, and the District of Columbia.
Mr Romney could count by contrast on just 206 from 24 states that are strong Republican territory or lean right.
The distance that must be made up in the battleground states to the magic 270-mark is thus far greater for one than the other.
"It's going to be great to feel the power of your votes and voices tomorrow," Springsteen told the 18,000 supporters here who had begun queuing in the streets in the pre-dawn hours, before launching into his vocal and mouth organ melody "Promised Land".
Nothing has bothered Mr Obama more than Mr Romney trying to usurp the "change" mantle that he claimed for himself in 2008.
On the trail he has flattered Mr Romney with faint mockery as merely a salesman.
"We know what change looks like, Madison, and what he's selling isn't it … I know what real change looks like … because I have fought for it, you see the scars I have earned for it and you have seen the grey hairs on my head."
Some in Team Obama, which saw the President hold one final rally in Des Moines, Iowa, last night, the state that launched his Hope and Change dream in the caucuses of 2008, still don't want to jinx what they are daring to spy. Superstition is hard to shake and some among them are refusing to shave until the votes are all in.
But one other bristly consigliore of the President looked this reporter in the eye here and said: "We feel good, we feel good."What song was Mr Obama jiving to in Ohio? "Signed, Sealed, Delivered".
Maybe Mr President. But not quite yet.
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