Hillary Clinton appeared to have defied the polls and even her own expectations as early projections from the New Hampshire primary showing her locked in a tight, too-close-to-call, contest with her Democratic rival Barack Obama.

But there was a clear victor in the Republican race with John McCain telling a euphoric crowd that he was the "real come-back kid" after American television networks declared he had beaten off a challenge from Mitt Romney. "Mac is back! Mac in back!" chanted supporters who believe he can kick on from here to win the nomination.

There is now a growing sense that the historically-charged battle between Mrs Clinton – seeking to become first woman to win the White House – and Mr Obama, who hopes to be the first black president, is far from over.

With around 60 per cent votes counted, Mrs Clinton had 39 per cent support and Mr Obama on 37 per cent and analysts pouring over data from exit surveys could not decide who was the winner. Her aides were already arguing that anything less than a decisive victory for Mr Obama should be treated as a defeat.

A race like a crackpot Dynasty

The contest between Barack Obama and Hillary Clinton matches any fiction

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Turnout was swelled by warm – almost spring-like – weather with state officials predicting an "absolutely huge" vote of 500,000 or more which would smash previous records. By early afternoon town clerks were already requesting additional ballot papers for the Democratic contest.

Exit polls suggested one in seven voters had made up their mind on the day of the election while around 40 per cent of those taking part in the Democratic contest were registered Independents.

Some aides to Mrs Clinton had been telling her to effectively cede coming contests in Nevada and South Carolina later this month, suggesting it would be more prudent to concentrate time and resources in California, New York and nearly 20 other states in what amounts to a national primary in early February.

But the former Iowa Governor, Tom Vilsack, who serves as a national co-chairman on the Clinton campaign, said he believed she would now regain her footing.

"All the candidates have been gunning at her, and that dynamic changes now," he said. "When people begin asking the same questions of Senator Obama, this will be a race for a long time."

Mr McCain's projected victory – by a margin of around 6 per cent over Mr Romney – 37 per cent to 31 per cent - represents an extraordinary resurrection for a candidate who was widely written off in the summer.

Today he flies into the next Republican battlegrounds of Michigan and South Carolina, hoping to gather further momentum in a nomination contest, which has become tangled with a succession of frontrunners stumbling over each other in recent weeks.

"We showed the people of this country what a real comeback looks like," Mr McCain said. "We're going to move on to Michigan and South Carolina and win the nomination."

Mr Romney, whose strategy of spending heavily on the early states appears now to be in tatters, will also head to Michigan – which votes next Tuesday – a state where his father was governor.

Mike Huckabee was in third place with just over 10 per cent of precincts reporting early, while Rudy Giuliani and Ron Paul vied for fourth.

The Republican field, which continues to have at least five viable candidates, meets for another TV debate on Thursday night in South Carolina, where Mr Huckabee, the Iowa winner and former Arkansas governor, and Fred Thompson, another Southerner, are hoping for do well.

Mr Giuliani is continuing his high-risk strategy of focusing on the later, delegate-rich states such as Florida and New York. He waved off questions today about his slide in the polls, insisting he is still ahead in 15 states.

On the Democratic side, polls had shown Mr Obama with a double-digit lead. But early returns suggested that Mrs Clinton could claim to have defied the pundits and the odds just as her husband did 16 years ago when he claimed a surprise second place in New Hampshire and went on to win the White House.

Mr Obama today had urged his idealistic young supporters to keep up the momentum generated by stunning victory in Iowa last week, saying: "The American people have decided for the first time in a very long time to cast aside cynicism, to cast aside fear, to cast aside doubts."

He added: "Today, it is your turn to stand up and be counted. Today, you have your turn to say that you are fed up with the petty politics of Washington.”

Mrs Clinton spent election day promising she would carry the fight on even if polls – showing she was heading for a second substantial defeat – were proved right. She vented fresh frustration at what she regards as hyperbole surrounding Mr Obama, saying: "At some point the free ride ends.”

Rumours were swirling around New Hampshire that she is preparing to shake-up her much-criticised campaign team, as well as begin a more aggressive pursuit of Mr Obama.

Maggie Williams, a longtime Clinton confidante, was reportedly being brought in to co-ordinate activities. Roy Spence, another family friend, was also said to be lined to play a big role in the next stage of a campaign increasingly focused on February 5 – "Super Tuesday" – when half the delegates for the Democratic Convention in August will be chosen.

Bill Clinton earlier launched one last fusillade in New Hampshire where as the "comeback kid" he had revived his own presidential hopes 16 years ago. He attacked the media for failing to ask Mr Obama, who has repeatedly highlighted his opposition to the Iraq war, about comments made in 2004 suggesting he did not know which way he would have voted. "Give me a break," said the former president. "This whole thing is the biggest fairy tale I've ever seen."

Mr Obama responded swiftly, saying: “I remember during the summer when we were down 20 points and I was getting knocked around pretty good, and I didn’t hear the Clintons’ camp complaining about how terrible the press was.”

Mrs Clinton's aides were said to be irritated by her husband's election day intervention, rekindling questions about whether he has become a loose cannon in her campaign. One aide was quoted expressing concerns that his comments would overshadow positive reaction to Mrs Clinton's eyes welling with tears on Monday – an apparently spontaneous show of emotion from a candidate often seen as calculating.

Mr Obama was today buoyed by supportive words from Colin Powell, President Bush's former Secretary of State, who said he was impressed and "terribly excited" by his fellow African American's bid for the White House.

Although Mr Powell stopped short of formerly endorsing the Democratic candidate, Mr Obama is widely expected to receive the backing of a powerful union in Nevada which could tilt the state's caucuses on January 19 his way.

John Edwards, second placed in Iowa, has been accused by Mrs Clinton of having a "buddy system" going with Mr Obama following his robust of her this week. Yesterday, however, he switched tack – saying neither Mrs Clinton nor Mr Obama would deliver the "real change" America needs.

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