President Barack Obama has cast his ballot early on Thursday, returning to his hometown of Chicago to drum up support for early voting.

The president said that "all across the country we're seeing a lot of early voting," adding that it was "really convenient" but joked, "I can't tell you who I voted for."

Obama signed forms and showed his driver's license at a South Side Chicago voting site and then voted at a blue voting machine.

It was the first time a sitting presidential nominee voted early and reflects the Obama campaign's strategy to encourage as many voters as possible to vote early or by absentee ballot.

About 35 percent of the electorate is expected to vote before Election Day.