Bush and Kerry in sprint to the finish

George Bush and John Kerry were fighting to the wire today as the longest and costliest election in American history threatened to end in deadlock.

At the end of a marathon battle that has seen £325million spent on advertising - triple the amount four years ago - the polls were all showing the same result, an election too close to call.

President Bush scheduled an extra stop in Columbus, Ohio, today instead of flying directly to the White House after voting near his ranch in Crawford, Texas. In a final appeal he promised "a safer America and a stronger America and a better America".

Mr Kerry was due to meet voters at a polling station in Wisconsin this afternoon before jetting to Boston to vote. In his last rally, in Orlando, Florida, he appealed: "This is the moment where the world is watching. All of the hopes and dreams of our country are on the line today."

But neither man has achieved momentum in the past week, which was dominated by the Osama bin Laden video and a row over 380 tonnes of missing explosive.

Out of 10 polls completed in the past two days, seven showed Mr Bush slightly ahead, two put Mr Kerry in the lead and one showed a dead heat. Overall, Mr Bush had an average lead of 1.5 per cent - statistically meaningless.

In the three key states where the battle will be won or lost, the gaps were rivetingly narrow. In Florida, the scene of the hanging chads fiasco in 2000, a Zogby poll predicted a dead heat at 48 per cent each, while a Fox News survey claimed Kerry was ahead by five points. But two other polls said Mr Bush was winning, one by as many as eight points.

Mr Bush looked more secure in his key target state of Ohio, with four out of five last-minute surveys putting him ahead by an average of two points.

But fierce legal battles were brewing in Ohio, with Democrats accusing Republican officials of discouraging minority voters while Republicans alleged widespread voter registration fraud. With 17,000 lawyers on standby to challenge close contests, there was speculation of a repeat of the deadlock four years ago that held up the election outcome for a month.

In Pennsylvania, the third biggest battleground state, two polls today put Mr Kerry ahead by one and four points.

Knife-edge polls, with leads of under two points, were also emerging from a series of smaller key states.

In one state, South Dakota, the parties were said to have spent $37 per voter in their efforts to clinch victory.

Frantic efforts to get people to vote continued today, with two million volunteers plus 250,000 paid professionals pounding phones and pavements to organise high turnouts among supporters.

Unprecedented high levels of early voting - thought by analysts to be a good sign for the Democrats - have already been seen in some key states.