Washington - Pennsylvania became the largest swing state to be called for Democratic presidential candidate Barack Obama over Republican John McCain, US networks projected, as voting booths closed in a series of key states on Tuesday. Results were also streaming in from other battlegrounds including Virginia, Florida, Ohio, North Carolina, Indiana and Colorado, marking the beginning of the end of a historic election day in the United States.
Pennsylvania and New Hampshire were projected to be captured by Obama, according to US networks. Pennsylvania, with 21 electoral votes, had been considered McCain's best shot of capturing a reliable Democratic state.
McCain had also hoped to steal New Hampshire and its 4 electoral votes after the state, known for its independent streak, relaunched his own candidacy in the primaries in January.
Georgia, a reliably Republican southern state that Obama thought he might have a chance to steal, was projected for McCain.
A series of other party strongholds were also called for both candidates, including South Carolina, Oklahoma, Tennessee, Alabama and Kentucky for McCain. Obama's wins so far include Massachusetts, New Jersey, Connecticut and his home state of Illinois.
Obama held an edge in Florida and McCain led in Virginia, with more than 40 per cent of precincts reporting in each state.
The country's state-by-state, winner-takes-all US electoral system, requires presidential campaigns to focus on key battleground states. A total of 270 electoral votes is needed to win the country's election.
The Obama campaign was satisfied with results so far, including voting procedures and early results from several states, said David Axelrod, chief political advisor to Obama.
Speaking to CNN, Axelrod said things were going so well that his main worry was that he "can't exactly figure out what should be giving me heartburn right now."
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.
Obama held his final campaign rally Monday night in front of 90,000 supporters in Manassas, Virginia, another battleground state, and was in Indiana Tuesday to meet with voters.
In Chicago, tens of thousands of people were already gathering after dark for Obama's election night rally in the city's downtown Grant Park. The disproportionately young crowd had a large representation of both whites and blacks, with small numbers of Latinos and Asians.
Tiffany Gholar, 29, a Chicago student and executive assistant, said that Obama's victory "would make me feel like some real progress has been made since the civil rights movement."
McCain's campaign was holding a rally at a Phoenix hotel.
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.
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.
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.
