Voting begins in US state of Ohio
John McCain and running mate Sarah Palin campaigned in Ohio on Monday
Early voting is getting under way in the US battleground state of Ohio, five weeks exactly before the 4 November presidential election.
It comes a day after Ohio courts ruled that new voters could register and cast an absentee ballot on the same day.
Republicans, who argue same-day voting opens the door to voter fraud, opposed the measure; Democrats backed it.
Both John McCain and Barack Obama have been campaigning hard in Ohio, seen as a key swing state.
John McCain, accompanied by running mate Sarah Palin, used a rally in Colombus, Ohio, on Monday to attack his Democratic rival over his economic policies.
Mrs Palin, Republican governor of Alaska, is preparing for the vice-presidential debate scheduled for Thursday night, in which she and Democrat Joe Biden will face each other for the first time.
She has come under increasing pressure after a series of TV interviews which critics say have exposed her lack of readiness for the role.
Monday's Ohio Supreme Court decision, backed by two federal judges, cleared the way for same-day registration and voting during a week-long period up to 6 October, when voter registration ends.
The Democrats hope the same-day voting period will benefit Mr Obama
The ruling was welcomed by state Democrats, who hope to encourage college students and other groups such as minorities, the poor and the homeless to make use of the same-day voting period.
Previously, voters had to be registered for at least 30 days before receiving an absentee ballot, which tended to reduce participation among such voter groups. They often favour the Democrats.
The ruling was seen as a victory for Ohio Secretary of State Jennifer Brunner, a Democrat, who had been criticised by Republicans for telling county election organisers to allow same-day voting.
Both Mr Obama's campaign and the Republican National Committee have urged supporters to make use of Ohio's 35-day early voting period to cast their absentee ballots.
Ohio was an important swing state in 2004, when it went to President George W Bush by a narrow margin, helping him to re-election.
A number of states, including the battleground states of Iowa, Virginia, Nevada, New Mexico and North Carolina, allow early and absentee voting.
Some voters prefer it because they fear potential problems and long queues at polling stations on election day.
The Obama campaign believes its strong on-the-ground organisation in many states could give it an advantage in encouraging people to cast their ballot early.