President Barack Obama and his Republican rival Mitt Romney have begun a crucial swing through key battleground states that will determine who wins Tuesday’s vote.

Barack Obama campaigns in Ohio, Wisconsin, Iowa and Virginia on Saturday, while Mitt Romney targets New Hampshire, Iowa and Colorado.

Both candidates will visit the Iowa town of Dubuque within hours.

Opinion polls suggest the rivals are almost tied, although Barack Obama is slightly ahead in most swing states.

Barack Obama, addressing crowds of Democratic supporters in Mentor, Ohio, said the election was a choice “about two different visions for America: the top down vision that crashed the economy, or a future built on a strong and growing middle class”.

Republican MItt Romney, opening his three-state campaign day in New Hampshire, said: “Let me tell you what I’d like to tell you: Vote for love of country. It is time we lead America to a better place.”

These frantic last days mark a punishing sprint at the end of a long marathon.

On the eve of the election, the pendulum appears to be moving towards Barack Obama, as the opinion polls are not shifting in Mitt Romney’s favor in enough battleground states.

Barack Obama has arguably had the better of the past week, given Friday’s moderately good news on the employment front and the wide praise of his handling of the aftermath of Storm Sandy. He also won the endorsement of independent New York Mayor Michael Bloomberg.

Barack Obama and Mitt Romney target key swing states as latest polls suggest they are almost tied

Correspondents say Mitt Romney has the tougher task for victory on Tuesday, as he must win a majority of the nine most keenly contested states.

But Barack Obama’s opinion poll lead in all the swing states is within the margin of error and Tuesday’s vote is likely to be close.

The election is run using an electoral college. Each state is given a number of votes based on its population. The candidate who wins 270 electoral college votes becomes president.

Ohio is proving to be a tough battle and, with 18 college votes, could prove a tipping point.

Barack Obama began his Saturday campaigning in the Ohio town of Mentor, while Mitt Romney staged his biggest rally of the campaign so far – 18,000 people – in West Chester on Friday.

Mitt Romney was joined by former primary rivals Rick Santorum and Rick Perry, as well as the defeated 2008 presidential candidate John McCain.

He said: “We’re almost home. One final push will get us there. The door to a brighter future is there, it’s open, it’s waiting for us.”

The Republican, whose main manifesto pledges are lower taxes and a $500 billion federal budget cut by 2012, said Friday’s jobs report was actually a “sad reminder that the economy is at a virtual standstill”.

Barack Obama has held mid-range rallies so far but plans to increase the size over the weekend, when he will be joined by former President Bill Clinton in Virginia on Saturday and in New Hampshire on Sunday.

The president campaigned hard in Ohio on Friday, highlighting his decision to bail out indebted US car makers in 2009, a move that was politically unpopular but which he says helped restore the industry.

Barack Obama’s manifesto sets out tax rises for the wealthy and more funding for job creation.

Mitt Romney has tried to make inroads into Pennsylvania, where opinion polls suggest the Democrats lead by four to five points but which would be a crucial boost to his chances if he could secure its 20 college votes.

The Republican challenger has also wooed Michigan and Minnesota, forcing the Democrats into late advertising there.

Early voting has been a key focus of this presidential election – some 25 million voters have already cast ballots in 34 states and the District of Columbia.

Some states have released the affiliation of early voters, giving Barack Obama an edge in Florida, Iowa, Nevada, North Carolina and Ohio, while Mitt Romney is favored in Colorado.

However, the figures suggest Barack Obama does not have the lead he had over John McCain four years ago.

Nevertheless, the Obama team has released data showing that two-thirds of those who have voted early are women, young people, blacks and Hispanics – demographics the Democrats say favor them.

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