US President Barack Obama has cast his ballot for the 6 November election in his hometown of Chicago and encouraged others who could vote before election day to follow his example.

Mr Obama went to an early-voting facility to show his driver's license before making his pick for president.

"I'm just glad I renewed my driver's license," he said after a poll worker asked to see his photo ID.

When he handed it over, she studied it closely.

"For all of you who have not yet voted early, I just want everybody to see what an incredibly efficient process this was," he said to journalists afterward.

It was the first time a US president had cast his vote early.

Scenes of presidential candidates and their spouses voting on election day are typically a ritual that ends a long campaign season.

First lady Michelle Obama has already cast her vote. The president has said, with mock relief, that she voted for him.

Both Mr Obama and Republican rival Mitt Romney are stressing early voting more than ever, encouraging their backers to take advantage of opportunities in many states as a means of increasing turnout.

However Mr Obama's team said statistics show he is benefiting the most from early turnout.

Obama campaign spokeswoman Jen Psaki said the campaign's early-voting margins were ahead of where they were in 2008 and beating Mr Romney.

The president was winning the early vote in the battleground states of Iowa, Ohio and Wisconsin, and had a 15- to 35-point lead among those who have already cast their votes.

"This is a major part of our on-the-ground programme and focus, and we hope that having the president do this today will send a message to people across the country, in states where early vote is an option, that this is something they should do, too," Ms Psaki told reporters on Air Force One.

"He has a busy life; many American people have busy lives - picking up their kids, taking their kids to soccer, working double shifts. And this is a great option to participate in the process," she added.

Mr Obama's stop in Illinois - which he is expected to win easily - was part of a two-day, eight-state marathon campaign trip that included Iowa, Colorado, California, Nevada, Florida, Virginia and Ohio.

Mr Romney is also engaged in a multi-state tour as he attempts to convince those who are still undecided to vote for him.