Barack Obama gestures during a visit to a campaign office in Chicago on the morning of the election (AP)
US President Barack Obama and Republican challenger Mitt Romney have left voters on election day with a stark choice between their fundamentally different visions for the country's future, laid out during an aggressive and closely fought battle for the White House.
Both sides cast the decision as one with far-reaching repercussions for a nation still recovering from the biggest economic downturn since the Great Depression and at odds over how big a role government should play in solving the country's staggering debt and high unemployment.
After months of campaigning and billions of dollars spent in the battle for leadership of the world's most powerful country, Mr Obama and Mr Romney were in a virtual nationwide tie, a symptom of the country's vast partisan divide.
Mr Obama appeared to have a slight edge, however, in some of the key swing states such as Ohio that do not vote reliably Democrat or Republican. That gives him an easier path to reach the 270 electoral votes needed to win the presidency. "I feel optimistic, but only cautiously optimistic," Mr Obama said. "Because until people actually show up at the polls and cast their ballot, the rest of this stuff is all just speculation."
Mr Romney told Ohio voters to remember as they go to the polls that the country is hurting financially under Mr Obama's policies. "If it comes down to economics and jobs, this is an election I should win," Mr Romney said.
Mr Romney cast his vote near his Massachusetts home on Tuesday morning. The Republican challenger still had election day rallies in Ohio and neighbouring Pennsylvania, traditionally Democratic territory where Mr Romney has made a surprise and last-minute push - perhaps against all odds - to compensate for Mr Obama's expected victory in Ohio.
Mr Obama voted last month, a move intended to encourage early voting that tends to favour Democrats. The president was spending election day in his home town of Chicago, where he was met with applause and tears from volunteers as he entered a campaign office before picking up a phone to call voters in Wisconsin. He later congratulated Mr Romney "on a spirited campaign" and told reporters he is "confident we've got the votes to win."
Under the US system, the winner of the presidential election is not determined by the nationwide popular vote but in state-by-state contests. The candidate who wins a state - with Maine and Nebraska the exceptions - is awarded all of that state's electoral votes, which are apportioned based on representation in Congress.
It is not just the presidency at stake: all 435 seats in the House of Representatives, a third of the 100 Senate seats, and 11 governorships are on the line, along with state ballot proposals on topics ranging from gay marriage to legalising marijuana. Democrats were expected to maintain their majority in the Senate, with Republicans doing likewise in the House, raising the prospect of continued partisan wrangling no matter who might be president.
In surveys of the battleground states, Mr Obama held small advantages in Nevada, Ohio, Iowa and Wisconsin - enough to deliver a second term if they held up, but not so significant that they could withstand an election day surge by Romney supporters. Mr Romney appears to be performing slightly better than Mr Obama or has pulled even in North Carolina, Virginia and Florida. No Republican has ever won the White House without carrying Ohio.