"Governor Romney has been out here making a lot of last-minute promises lately," the president told a crowd of 8,500 gathered in front of a school in the city of Nashua.
"Said he's all about fighting for the middle class. Said he would cut taxes for everybody," he said. "But the problem is, we heard those promises before."
Meanwhile at a campaign event in the town of Kissimmee, Florida, Romney urged the crowd to take advantage of the opportunity they have beginning on Saturday to cast their ballots.
"Early voting began today, that means today you can go vote, and it helps for you to vote now because the earlier you vote, the more help you can give us to get people to the polls," he said, adding "we're going to have to turn out our people".
The message for the Republican candidate resonated with Luis Maldonado, 38, a Florida electrician, who said he believes Romney can fix the ailing US economy. "I believe in the plans that he has," he said.
"In the past four years we haven't seen what we were expecting from the president. I believe he's going to create more jobs," Maldonado said.
The start of early voting on Saturday in Florida, Maryland, and Washington, DC brought long lines of voters who in some cases wrapped around city blocks.
So far, at least 11 million people have already cast their ballots in states where early voting is under way, according to a tally by experts at George Mason University near Washington.
Analysts said early voting this year is on track to beat the record set in the 2008 presidential elections, when more than 30 per cent of ballots were cast before election day.