Washington - Voting booths closed in key eastern states on Tuesday that could decide whether Republican John McCain or Democrat Barack Obama captures the White House.

Polls closed in battlegrounds including Virginia, Ohio, North Carolina, Georgia and Indiana and official results were already trickling in, marking the beginning of the end of a historic election day in the United States.

Millions of voters waited for hours at polling stations across the country Tuesday as McCain and Obama made a final push for votes in swing states.

McCain campaigned in Colorado where he claimed he had regained momentum and expressed confidence that he would defeat Obama when all the ballots are counted.

McCain has campaigned aggressively in the last days of the election in states like Colorado, Pennsylvania, Florida and Indiana, where polls had shown that the race was tightening. He later flew back to his home state Arizona to wait for the results.

Obama held his final campaign rally Monday night with 90,000 supporters in Manassas, Virginia, another battleground state, and was in Indiana Tuesday to meet with voters. By the evening he was back at his campaign headquarters in Chicago to watch ballot returns.

Officials were prepared for an unprecedented turnout as voters delivered their verdict on Obama, 47, and McCain, 72, after the longest and most expensive campaign in US history.

Democrats are hopeful that eight years of President George W Bush's unpopular policies in Iraq and the slumping economy will persuade voters to hand them control of the White House and strengthen their control of Congress.

The faltering US economy was by far the top concern of voters heading to the polls in Tuesday's general election, according to initial exit polls by US broadcaster CNN.

A full 62 per cent of voters ranked the economy as the key issue of this election, compared to 10 per cent invoking the war in Iraq and 9 per cent rating terrorism or health care highest.

If elected, Obama would be the first African American president in US history. If McCain wins, he will be the oldest president ever to begin his first term.

But in the state-by-state, winner-takes-all US system, presidential campaigns focus on key battleground states, and McCain was still hoping to pull off an upset victory by winning in states like Ohio, Florida and Pennsylvania. Polls were set to close in the latter two states at 8 pm (0100 GMT).

A total of 270 electoral votes is needed to win the election. Democratic stronghold Vermont and Republican stronghold Kentucky were already called by US networks for Obama and McCain respectively. Fox News projected West Virginia for McCain.

Millions already voted in recent weeks for early or absentee voting allowed in 31 states, including key battlegrounds Florida, North Carolina, Colorado and Nevada.

Voters waited patiently in serpentine queues early Tuesday to cast ballots. Many had started lining up before dawn, some braved pouring rain to cast their ballot.

According to tradition, voting began at the stroke of midnight Tuesday in a handful of remote towns in the north-eastern state of New Hampshire, where the residents of Dixville Notch - who have voted Republican since 1968 - gave Obama an upset, with 15 votes versus six for McCain.

It was a bittersweet end to the 21-month campaign for Obama: His grandmother Madelyn Dunham, 86, passed away after a battle with cancer, the Illinois senator revealed Monday.

An aggregate of major national polls compiled by realclearpolitics. com gave Obama 51.9 per cent to McCain's 44.4 per cent on Tuesday. (dpa)