Republican John McCain and Democrat Barack Obama battled yesterday in states that voted Republican in 2004 in the final, frenetic weekend of a long and grinding US presidential election campaign.

McCain was in Virginia looking to turn out the vote on Tuesday in a state that normally votes Republican but appears to be siding with Obama. "We need to win Virginia on the fourth of November and with your help we're going to win," a spirited McCain said, exhorting supporters to "volunteer, knock on doors."

"With your help, we can and will win," he said. "We're coming back and we're coming back in Virginia."

Obama, enjoying a lead in national polls and in many key battleground states where the election will be decided, sought a knockout punch in three states that went for President George W. Bush in 2004 - Nevada, Colorado and Missouri.

Nowhere to be seen on the campaign trail was Bush himself. With a popularity rating below 30 per cent, Bush was not asked to campaign for McCain. Obama has consistently sought to portray his opponent as a Bush clone.

Americans on Tuesday will vote in what amounts to 51 separate elections in each state and the District of Columbia.

Each state has a number of electoral votes based on the size of its representation in Congress. Whichever candidate gets 270 electoral votes wins the White House.

They will choose between Illinois Senator Obama, 47, who would be the country's first black president, and Arizona Senator McCain, 72, the former Vietnam prisoner of war who would be the oldest person ever elected to a first presidential term.

If current polling is accurate and stands up on Election Day, Obama will win, possibly by a comfortable margin.