US President Barack Obama raced back to the White House Monday ahead of Hurricane Sandy, which threw election endgame plans into turmoil just one week before he asks Americans for a second term.

Democrat Obama ditched plans to appear with ex-president Bill Clinton in Florida to steer a huge government relief effort as high winds and torrential rains began to lash the northeastern US.

Millions of people faced the prospect of damage from falling trees, severe flooding and power outages, including in some key swing states like Virginia, where Sandy's "October Surprise" may have an unpredictable electoral impact.

Grabbing a chance to leverage the built-in advantages of incumbency, Obama made clear his focus, until Sandy had barreled through, was the safety of Americans, not his own immediate political fate.

"Obviously my first priority has to be to make sure that everything is in place for families," the president told campaign workers in Florida late Sunday.

The president had been due to appear in Florida, Ohio and Virginia, and also scotched plans to head to Colorado, another swing state, on Tuesday.

Republican Mitt Romney also altered his plans as he tried to drive recent momentum right up to polling day on November 6, seeking to fracture Obama's "firewall" of midwestern states and deprive him of a second term.

The Republican instead canceled rallies in storm-threatened Virginia and went instead to inland Ohio, the Midwestern epicenter of the unpredictable final week battle for the White House.

The storm's immediate political impact was unpredictable, but it was expected to bring dire conditions to Virginia and also could impact other swing states including Ohio and New Hampshire, and depress early voting elsewhere.

"Obviously we want unfettered access to the polls because we believe that the more people come out, the better we're going to do," senior Obama advisor David Axelrod told CNN.

Romney aide Kevin Madden said his boss had already got his message across to those in the hurricane's path and said the safety of voters and their families was now the priority.

Romney got good news Sunday when a poll showed him tied in all-important Ohio and he captured the endorsement of the Des Moines Register newspaper in Iowa.

But a new poll in Virginia, which carried by the Washington Post and ABC News, had Obama leading by four points, compared to previous surveys showing a tied race.