The presidential candidates have squeezed as many campaign appearances as possible into the final days ahead of Tuesday’s election.
Nationwide polls show the men to be locked in one of the closest presidential races in recent American history.
A majority of polls in the battleground states – including Iowa, Wisconsin and Ohio – show Mr Obama with a slight advantage, giving him an easier path to the 270 electoral votes needed for victory.
Meanwhile, Mr Romney will visit Sanford, Florida; Lynchburg, Virginia; Fairfax, Virginia; Columbus, Ohio; Manchester, New Hampshire; before heading to Boston.
The two rivals criss-crossed the country on Sunday, pushing hard on the campaign trail’s home straight.
Both candidates pressed their arguments about why they offer the best solution to a weak US economy and partisan gridlock in Washington.
The two also made direct appeals for votes in a race that may come down to which side does the best job of getting its supporters to the polls.
“It’s up to you. You have the power,” Mr Obama told a crowd of more than 14,000 people who filled the downtown streets of Concord, New Hampshire.
“You will be shaping the decisions for this country for decades to come, right now, in the next two days.”
In Iowa, Mr Romney urged more than 4,000 people in a Des Moines hall to get out and vote.
He also tried to convince undecided or former Obama supporters to back him on Tuesday.
At a later stop in Ohio, Mr Romney said: “Let’s make sure that we get everyone to the polls.”
The Romney campaign has also launched an 11th-hour push to win Pennsylvania.
On Sunday, the Republican candidate rallied thousands of people in the cold, telling voters he was going to win the state.
The Republican nominee had visited Pennsylvania during the general election campaign, but began making a significant play in the state last week.
His campaign bought millions in TV advertising and scheduled the late rally in the Philadelphia suburbs just a few days in advance.
After rules regulating campaign funding were eased for this election, the two political parties ploughed huge amounts into primarily negative advertising against the opposition.
Americans in the key states have been hit by a blizzard of campaign ads in recent weeks.
Would-be voters have been bombarded with some 40% more television advertising in the lead up to this election, compared to those in the 2008 election period.
The advertising in 10 strategic states has cost more than \$1bn (£620m).