Polling stations are beginning to close in some parts of the United States as Americans vote in mid-term elections to decide who will control both houses of Congress.

In an election filled with tight races, all 435 seats in the House of Representatives are up for grabs in the nationwide vote, along with 34 seats in the 100-member Senate and 36 of the 50 state governorships.

President George W Bush and his wife Laura voted at a fire station close to their ranch in Crawford, Texas.

Mr Bush gave a thumbs-up to reporters, but then turned his thumb sideways, indicating the uncertainty over the results.

	:	US poll results
Click here for a state-by-state guide to seats

He again urged all Americans to use the ballot.

"I'm encouraging all people across this country to vote," he said.

Mr Bush later boarded his plane to return to Washington for what was expected to be a long night of results from many close races.

Voting has finished in several eastern states, but the media were expected to be cautious in projecting winners after the consortium that conducts exit polls said some of its results were unreliable.

In Virginia, Senator Jack Warner, a Republican unopposed by a Democratic candidate, cruised to his fifth consecutive six-year term.

Elections 2002

All 435 House seats contested - 218 needed for majority 34 Senate seats contested - 51 needed for majority 36 governorships at stake Polls close at 0500 GMT on Wednesday on the west coast Many key states are so close that final results may take days

In Kentucky, Republican Senator Mitch McConnell won his fourth consecutive term, with more than 60% of the vote.

Despite the fact that both parties have spent record-breaking money on campaigning, overall voter turnout had been predicted to be low.

But election officials in several states have reported higher-than-expected turnout for some hotly-contested races.

Much of the focus is on the agonisingly close race for the Senate, where the Republicans and Democrats are tied with 49 seats each - with two independents.

Traditionally the party holding the White House loses seats in the mid-terms, but Mr Bush has been campaigning feverishly to buck that trend.

Whirlwind tour

Many eyes were on Florida, where balloting problems marred the 2000 presidential race and the 10 September primary election.

As voting began, one elderly woman triumphantly brandished her voter registration card at a polling station in Miami Beach, shouting "last time I couldn't vote".

Democrats had vowed revenge against Governor Jeb Bush, the president's brother, who is seeking re-election - but early reports showed him with a healthy lead over Democrat challenger Bill McBride.

In Minnesota, where the former Vice-President Walter Mondale is standing, officials were being extra diligent. When Mr Mondale reached the front of the queue to vote, they asked him what his name was.

Meanwhile, the Voter News Service, a consortium run by major media outlets that conducts the exit polls used to project winners, decided not to release much of its data, blaming a computer bug.

But the service, which was revamped after the 2000 presidential cliff-hanger, was still expected to report on the actual vote count, and might provide some limited exit-poll data.

In a whirlwind tour to drum up support Mr Bush has visited 17 cities in 15 states in just five days.

He is all too aware of just how crucial and how close-run the vote is.

Democrat control of the Senate has hindered much of Mr Bush's policy agenda and could harm his re-election campaign in 2004.

Republicans will also try to defend their slim 11-seat majority in the House of Representatives.

I think Bush has done a pretty darn good job so far Eric, USA

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If the Republicans do well, Mr Bush would be only the third president in a century to make mid-term gains, after Franklin Roosevelt in 1934 and Bill Clinton in 1998.

But the BBC's Justin Webb in Washington says if the Republicans do badly there is a risk that the blame might be directed at Mr Bush.

Analysts say results may not be immediately clear on Tuesday.

Recounts and legal challenges look a near certainty and our correspondent says the result might even be decided by the courts in the same way as the 2000 presidential election.

The Justice Department said more than 400 observers were monitoring the voting.