As polling centres in the U.S. open on Tuesday morning to decide who will sit in the White House for the next four years, over one-third of the voters have already exercised their franchise using the provision of early voting.

According to latest figured complied by the U.S. Election Project of the George Mason University, more than 30.5 million voters had already cast their ballots.

Barack Obama, who cast his vote through early voting along with First Lady Michelle Obama, led from the front as he became the first U.S. President to do so.

Long queues were seen in several key battleground states including Florida and Ohio, where people waited for several hours for their turn to cast their ballots.

Seeing the warm response by voters and the last minute rush on Monday, the project believes that the figures will cross the previous highest of 41 million recorded in 2008 polls.

Michael P. McDonald, an associate professor at the university, has projected that some 35 per cent of the total eligible electorates will case early voting this year.

In some States like Florida, more than half of the voters will have already cast their votes.

As the term indicates, early voting means casting vote before the Election Day either by mail or in person. The time and date of early voting varies from State to State.

Any U.S. citizen above the age of 18 is eligible to vote in the U.S. general elections. According to the project, in 2012 an estimated 219 million people are eligible to cast their votes. But those in prison, probation or in parole are debarred from voting.

An estimated 3.2 million — though having attained the voting age — are not eligible to vote because either they are in prison (1.6 million) or are on probation (1.32 million) or are on parole (about 630,000).

In 2008 the total number of eligible voters were 213.3 million of which of which, an estimated 132.65 million (62.2 per cent) exercised their right to franchise.

The total number of eligible voters who were then debarred from voting stood at 3.1 million.

In Florida, more than 4.5 million people had already cast their votes by Sunday.

The number was high in several other States as well with Colorado (1.7 million), Georgia (1.8 million), Iowa (640,000), North Carolina (2.7 million), Ohio (1.6 million), Oregon (1.1 million), Tennessee (1.45 million) and Texas (3.4 million), according to figures released by the project.

These votes will be counted along with the other votes on Tuesday evening after polling closes.

Meanwhile, recent opinion polls have revealed that Mr. Obama has a substantial lead among the early voters.

As the Romney campaign gained momentum after the first debate early October, Team Obama pushed people to go in for early voting.

This was one of the reasons why the Obamas opted to go for early voting.

“If you look at the early voting in Nevada, Iowa, Florida, Colorado, Ohio, we feel very, very good about the numbers that we’re mounting up in those states,” Obama strategist David Axelrod said during a conference call last week, which was quickly disputed by the Romney Campaign.

“They are under-performing their 2008 numbers and we are over performing,” Mr. Romney’s political director Rich Beesone said in a reaction.

“In Iowa, 40 per cent of Iowa votes have been already cast and President Obama leads among early voters by 23 points in the latest polls. This means that Mitt Romney needs to win the remaining votes by 23 points to tie President Obama on Election Day,” the Obama Campaign spokesperson, Jen Psaki told reporters abroad Air Force One on Monday.

“We’re ahead in early vote in almost every single swing state. We feel great about where our ground game is now. We feel great about where we’re closing this race. We know there’s a lot of fantasy talk happening from the Romney team about the number of electoral votes that they think they’re going to achieve. We’re not going to get into that kind of predictions,” she said.

Tuesday’s elections will not only elect the next President, but also all seats in the U.S. House of Representatives and one-third of that in the Senate.

In addition, the ballot paper will also ask people to vote on several key amendments, issues and topics varying from State to State.