The former first lady was cheered by new polls giving her a shot of staving off the Illinois Senator's latest attempt to knock her out of a race that threatens to split the Democratic Party.

Clinton, 60, started the day in North Carolina, where she is giving her rival a closer than expected race, before flying to Midwestern Indiana, where she is seen to need a win to quell calls for her to quit the race.

"Think about who you believe, think about who you can count on," Clinton told supporters at a fire station here in one of Indiana's Chicago suburbs.

"If you go vote for me tomorrow (Tuesday), I will never forget you."

Obama was up at dawn in Indiana, at a construction site, canvassing the kind of blue-collar voters who have sided with the former first lady in past contests, and frustrated his attempts to clinch the nomination.

"This is going to be a tight election here in Indiana, every poll shows a dead heat, we need every single vote," he said, before later heading to North Carolina on another get-out-the-vote mission.