President Barack Obama has taken big lead over Mitt Romney among voters who have already cast their ballots, according to Reuters/Ipsos polling data compiled in recent weeks.

Obama leads Romney by 59 percent to 31 percent among early voters, Reuters reports. The sample size is relatively small, but the president's margin is well above the poll's margin of error.

With the only 23 days away, 7 percent of those surveyed said they had already voted either in person or by mail.

Meanwhile, a Public Policy Polling survey released Saturday night showed Obama leading 51 to 46 percent in Ohio, little changed from two weeks ago. Gallup's daily national tracking poll released Sunday showed Romney leading 49 to 47 percent, unchanged for three days running.

 The Reuters online poll is another sign that early voting is likely to play an even bigger role this year than in 2008, when roughly one in three voters cast a ballot before Election Day. Voting is already under way in some form in at least 40 states.

Both campaigns are urging supporters to vote as soon as possible so they can focus their get-out-the-vote efforts on those who are still undecided or need more prodding to get to the polls.

Early voting was a big part of Obama's victory over John McCain in 2008, and his campaign aims to repeat that success this year.

The Reuters/Ipsos poll indicates the Democrats' efforts appear to be paying off, although their advantage could erode as Election Day approaches.

The Obama campaign says it is leading among early voters in Iowa and Ohio, and trailing by a smaller margin than 2008 in several other swing states. It expects its early voting efforts will help the campaign weather a blitz of negative ads expected to saturate the airwaves in battleground states in the final weeks.

The Romney campaign, however, says it is leading or even with Obama among early voters the vital states of Florida, North Carolina, Colorado, Nevada and New Hampshire. The campaign says it has seen a spike in volunteering and voter enthusiasm among Republicans since Romney's strong debate performance against Obama on Oct. 3.