Mitt Romney has promised to be the agent of change needed to restore US economic health, accusing President Barack Obama of a four-year policy failure that threatens to "crush our future".

With 10 days until Americans vote, the Republican nominee sought to steal Obama's 2008 "change" slogan and brand him a hapless leader, unable to end the slow-growth malaise that has defined the economy.

"The president's campaign falls far short of the magnitude of the times. And the presidency of the last four years has fallen far short of the promises of his last campaign," Romney, 65, told a crowd in Ames, Iowa.

Turning the tables on 2008 Obama, the multi-millionaire private equity baron billed himself as the hope-and-change candidate and the Democratic incumbent as representing the political "status quo".


"President Obama promised to bring us together, but at every turn, he has sought to divide and demonise. He promised to cut the deficit in half, but he doubled it," Romney said.

The election is on a razor's edge, with Romney ahead in national polls but still trailing in key swing states.

Both teams are preparing cross-country travel blitzes in the campaign's last 10 days but Mother Nature has intervened.

Hurricane Sandy threatens to barrel ashore along the US mid-Atlantic coast tomorrow, bringing torrential rain and heavy flooding, and potentially knocking out power to millions just a week before the election.

The storm could threaten millions of residents, upend election preparations in several states, interfere with early voting, and potentially cause problems at polling stations.

Meanwhile the Government released data showing economic growth picked up steam in the third quarter, reaching an annual pace of 2 per cent.

The rate was a little better than expected but Romney called the news "discouraging", saying growth was less than half what was predicted by the White House when it passed the 2009 stimulus bill.

"Slow economic growth means slow job growth and declining take-home pay. This is what four years of President Obama's policies have produced".

Romney said he could get the economy moving ahead at 4 per cent growth. Team Obama attacked Romney for "dishonest attacks and empty promises of change", but no new policy.