WASHINGTON, Oct. 28 (Xinhua) -- U.S. Democratic presidential nominee Barack Obama is leading his Republican opponent John McCain by 53 percent to 34 percent among early voters, a new poll indicated Tuesday.

    The poll was conducted by the Pew Research Center among some of the 12 million voters who have already cast ballots six days ahead of the presidential election day on Nov. 4.

U.S. Democratic presidential nominee Barack Obama greets supporters before delivering a speech in Canton, Ohio, October 27, 2008.

At present, 34 U.S. states allow voters to cast a ballot before election day, either in person at the polling site or by mail.

    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 Obama.

    Campaigns, voters and election workers have increasingly embraced early voting this year.

U.S. Republican presidential nominee Senator John McCain is joined by U.S. Republican vice-presidential nominee Alaska Governor Sarah Palin (L) and her husband Todd (2nd L) at a campaign rally in Hershey, Pennsylvania October 28, 2008.

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

    In 2004, 22 percent 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.

    Michael McDonald, a politic expert at George Mason University, said the early voting advantage for the Democrats may narrow because the Republicans typically start their mobilization efforts closer to election day.