Barack Obama shakes hands with supporters in Kent, Ohio (AP/Tony Dejak)
Barack Obama and Mitt Romney have returned to the crucial battleground state of Ohio with new polls showing the president edging ahead there.
A day after his address to world leaders at the United Nations, Mr Obama will speak at two universities in the Midwest state, hoping to generate the kind of enthusiasm among young voters that helped fuel his victory four years ago.
Mr Romney was making three stops in major cities during a bus tour aimed at drawing a contrast with Mr Obama on the economy, which remains the top issue for voters before the November election.
Both candidates in the tight race recognise how critical Ohio's 18 electoral votes will be. Losing the state would dramatically narrow Mr Romney's path to the 270 state-by-state electoral college votes required to win the White House - and no Republican has ever lost Ohio and won the presidency.
With early voting set to begin in Ohio on October 2, time is running out.
The candidates are also preparing for their first of three debates next week - the next chance for Mr Romney to make a high-profile, widely broadcast case for the presidency.
Mr Obama's visit marks his 13th trip to Ohio so far this year. Mr Romney has visited the state 10 times since May 1, with an additional seven visits during the earlier primary campaign.
The president has the edge in Ohio six weeks out from Election Day, helped by signs of an improving economy. Mr Obama has led Mr Romney in a series of recent polls in the state. A Washington Post poll on Tuesday showed Mr Obama with a lead that was outside the poll's margin of error. Even on handling of the economy, where Mr Romney until recently has had an advantage, Mr Obama now leads.
A new CBS/New York Times poll also showing Mr Obama ahead in the state and ahead in Florida, which along with Ohio is the most important of the 10 or so battleground states that will decide the election. Such states do not reliably vote Democrat or Republican and are the target of a dizzying amount of campaign ads.
For Mr Romney, Ohio was already challenging because of the state's better-than-average economy. The jobless rate in Ohio is almost one percent lower than the national average. Mr Romney and other Republicans credit Ohio's Republican governor, John Kasich, but the good news undermines Mr Romney's pitch that Mr Obama's policies are not working.