A woman arrives at the elections office to cast a ballot during early voting Wednesday in The Villages, Florida. AP

Ahead of the November 3 presidential election, the Democratic Party has gained an advantage against the Republicans in early voting due to a surge in absentee ballots cast in states across the US, it was reported.

According to official data released on Friday, over 6 million Americans have already cast their ballots in 27 states, reports The Hill news website.

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Michael McDonald, a political scientist at the University of Florida who analyzes early voting, said registered Democrats have returned 1.4 million ballots, more than twice the 653,000 ballots registered Republicans have returned so far.

About two-thirds of voters who have already voted — 3.7 million Americans — are either unaffiliated with either party or live in states that do not register voters by party.

A person casts a ballot for the upcoming presidential election during early voting in Sumter, South Carolina, on Friday. Reuters

Demographic modelling by prominent Democratic firm, TargetSmart, has estimated that almost 3 million of all votes cast have come from Democratic voters, compared to about 2.1 million from Republicans.

Regardless of party affiliation, more people are voting by mail this year than in years past due to the ongoing Covid-19 pandemic.

At this point in the 2016 presidential contest, only around 750,000 people had voted.

In Wisconsin, South Dakota and Virginia, early votes account for more than one-fifth of the total number of votes cast in the entire 2016 election, McDonald's data revealed.

Meanwhile, in states like Florida, North Carolina and Pennsylvania, Democrats have cast more votes than Republicans.