This article is more than 11 years old

This article is more than 11 years old

More than 12m of about 213m eligible American voters across the country have already cast ballots, sometimes waiting in queues around the block to do so, despite the election being six days away.

Barack Obama is leading 53% to McCain's 34% among those who have already voted, according to a poll released today by the Pew Research Centre.

Under a procedure known simply as early voting, 32 states allow voters to cast a ballot before election day, either in person at the polling site or by mail. An additional 14 states and Washington DC allow it if voters can argue they will be unavailable next Tuesday.

The long October queues at polling places anticipate a tremendous surge in voter turnout over previous elections, and statistics from key states indicate an advantage for Barack Obama over rival John McCain among early voters.

"If we're in an election year where you have to wait two hours to vote early, you can imagine what it will look like on election day proper," said Doug Chapin, an election expert at the Pew Centre on the States.

Campaigns, voters and election workers have increasingly embraced early voting this year. Voters enjoy the convenience. Election workers like early voting because it allows them to stress test election procedures while time remains to iron out flaws. It also lessens the crunch on election day.

Research indicates early voters tend to be more partisan and firm in their choices than average, and the campaigns of Barack Obama and John McCain have encouraged supporters to vote early.

The campaigns and their backers have dispatched volunteers and paid canvassers door to door to push supporters to the polls ahead of election day.

In Florida, where more than 2m have already cast ballots, Democratic vice-presidential candidate Joe Biden on Monday said an early vote could decide a close race.

"With an early vote, now is the time to choose," he said at a rally. Also on Monday, Michelle Obama launched a two-day swing through the western US to promote early voting.

Leading in national polling and in key battleground states, the Obama campaign hopes early voting will reduce the chances of a late surge by John McCain.

Also, if early voters discover a problem with their registration, there is time to correct it and lessen the risk of disenfranchisement, Obama campaign workers say. That is increasingly vital as states enact polling place identification requirements and voter-roll strictures.

"The more people we can get out, the fewer we have to deal with on November 4," said Faulkner Fox, an Obama volunteer organiser in Durham, North Carolina. "We can bank those votes."

In 2004, 22.5% of American voters cast their ballot before election day. That is expected to rise to as much as one third of all voters this year.

"The question remains if this means a greater share of the 2008 vote will be cast early, if turnout will be up overall, or - as I suspect - a combination of these two factors are in play," writes Michael McDonald, an associate professor of government and politics at George Mason University.

The long queues at early voting sites across the country seem to be benefiting the Democratic ticket. While the votes will not be counted until election day, the party registration statistics in key states anticipate an advantage for Obama.

In North Carolina, for instance, registered Democrats have cast 55% of early ballots, compared with 28% for the Republicans and 17% with no party affiliation, according to McDonald's analysis. In Florida, Democrats have cast 45% of early and absentee votes, compared with 40% for the Republicans and 15% other.

But the apparent early voting advantage for the Democrats may narrow because the Republicans typically start their mobilisation efforts closer to election day, McDonald told the Guardian.

One early vote the Democrats were happy to tout: George Bush last week cast his Texas absentee ballot for John McCain.