In a sign of the intense interest in the presidential race, about 500,000 Floridians have already cast absentee ballots and that number is growing by the day.

More than 1.8 million additional voters have requested the ballots, which are typically mailed in.

The heaviest voting so far is taking place in Tampa Bay, Miami-Dade and the so-called Interstate 4 corridor in the center of the state.

Generally, whoever wins the I-4 corridor — the swing area of the swing state — wins the election.

Overall, Republicans lead Democrats in the number of voted absentee ballots so far, by a 45-40 percent spread. That’s despite the fact that registered Democrats exceed Republicans by a 4-percentage-point margin in the state.

Democrats, however, say they’re happy with their absentee-ballot program, which is typically a Republican strength. Democrats trailed Republicans by 16 percentage points relative to this point in the 2008 election.

So both sides are claiming victory.

"Democrats know they have an intensity problem, so they’re putting lipstick on their pig by touting big increases in absentee ballot requests,” said Brett Doster, a Florida advisor for Mitt Romney. “Problem is, Republicans are still ahead in overall requests, and every day, Republicans have widened the gap in absentees returned.”

President Obama’s Florida spokesman, Eric Jotkoff, said the Democratic numbers reflect the campaign’s strong organization, which has encouraged some absentee-ballot voters to drop their ballots off at elections offices in person as part of the campaign’s “Vote Now!” effort.

“Floridians are fired up to reelect President Obama,” he said. “They’re casting their ballots in record numbers through vote-by-mail and by voting now through in-person absentee ballots at supervisor of elections offices.”

Not every Republican ballot is a vote for Republican Mitt Romney, nor is every Democratic ballot cast for President Obama. However, early voters tend to be the most partisan and vote the party line.

The big unknown: independent voters, who have cast more than 72,000 ballots and requested 347,000 more as of Wednesday morning.

In all, about 465,000 absentee ballots had been cast by Wednesday morning and, by day’s end, it’s likely the total vote hit the half-million mark, officials say.

Pinellas County voters had cast the most absentee votes in the state, at least 56,000 ballots, with Republicans edging Democrats by just a few hundred voters. Miami-Dade County, the state’s largest, cast the second-highest number of votes — 35,000 — followed by Hillsborough County, with 32,000.

Early in-person voting — typically dominated by Democrats — begins Oct. 27 and runs through Nov. 3. Because the GOP-Legislature shortened the number of early in-person voting days, Democrats have tried to encourage their supporters to cast more absentee ballots.

"If you combine absentees and early votes, in 2008, the Democrats were up 7 percent going into Election Day, and Obama still only won by 3 percent. As of today, Republicans are up 4 percent," Doster, the Romney advisor, said. “While the absentee request totals have improved for Democrats, the numbers show they are cannibalizing their early voters, and the net effect is that Republicans have a huge lead.”

Obama’s Florida spokesman said the campaign isn’t worried.

“Our grassroots army will continue working to encourage all Floridians to make their voices heard by casting their ballots through the several convenient and easy ways to vote in Florida,” Jotkoff said.