Millions of Americans cast their votes

The race for the White House is intensifying, with voters and politicians alike now eagerly awaiting the results of Super Tuesday.

Presidential hopefuls Hillary Clinton and Barack Obama joined millions of Americans casting their ballots on the biggest presidential primary day in US history.

Mrs Clinton voted in suburban New York, accompanied by her husband, former President Bill Clinton. Mr Obama headed back to Illinois after a round of television and radio interviews.

The Democrat battle between the two senators is on a knife-edge.

As electors in more than 20 states cast their votes, polls in key states including California, New Jersey, Arizona and Missouri show the pair are in a series of close races.

Mrs Clinton is still favourite but Mr Obama is being endorsed by stars like Stevie Wonder and Oprah Winfrey.

Delegate-rich California will be crucial, and Illinois senator Mr Obama has come from more than ten points behind just two weeks ago to draw level with Mrs Clinton.

New York, New Jersey, Arizona and Missouri will also be critical with hundreds of delegates available.

Because Democrats distribute delegates in proportion to their vote statewide and in individual congressional districts, candidates can come away with large numbers of delegates even in states they lose.

Aides for both campaigns predicted the contest would continue for weeks or months to come.

In contrast, many of the 21 Republican contests are winner-take-all when awarding delegates, meaning a strong day by John McCain could give him a commanding lead.

Republican Mike Huckabee claimed the first win on Super Tuesday - the biggest presidential primary day in US history.

Mr Huckabee, a Baptist preacher and former Arkansas governor, won in the second round of balloting at the West Virginia Republican convention as most John McCain voters switched to him to deny Mitt Romney a victory.

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