US presidential candidates Barack Obama and John McCain planned one final race across the country on Monday as state officials prepared for record turnout in Tuesday's general election.

As Chicago braced for a throng of 1 million people at a public park in anticipation of Democrat Obama's victory Tuesday, Republicans were wishing them bad weather and a surprise electoral victory for the underdog McCain.

'I hope the million or so people who are planning to gather in Chicago have a long, cold night,' quipped Mitt Romney, the former Massachusetts governor who lost his Republican bid for the presidential nomination to Senator McCain.

Although election results are expected to start coming in about 0100 GMT Wednesday, western states could play a big role this year, with results expected to filter in well after 0300 GMT.

With massive voter turnout of as much as 90 per cent expected and new equipment in many states, the night could get much longer before a winner can be declared.

McCain and Obama were storming through a combined 10 states on Monday to shore up narrow margins and get out the vote in swing states. Between them and their key surrogates, they were set to cover a total of 22 states.

Obama, who would be the first African American president in US history, was the strong favourite heading into Tuesday's vote. An aggregate of major national polls compiled by realclearpolitics.com gave Obama 50.7 per cent to McCain's 44.3 per cent as of Sunday night.

But nationwide numbers are less important than capturing states with big electoral votes in the US' indirect election method. Battleground states include Florida, Ohio, Pennsylvania and Virginia - which hasn't voted Democratic since 1964 but is leaning toward Obama.

In Chicago, volunteers from across the city were spending the campaign's final hours rallying the vote for fellow Chicagoan Obama, who represents their state of Illinois in the Senate.

The campaign had attracted help ranging from high school students to grandmothers to those who knew Obama as young man working as a community organizer in the city's poor neighbourhoods.

Seventeen-year-old volunteer Robert Stuart III said he knows his efforts at a Chicago phone bank are part of a crucial last-minute drive to get out the vote. 'If I wasn't hopeful, I wouldn't be here,' he said.

Obama was to hold his election night rally at Grant Part along windy Lake Michigan, normally an ice box at this time of year. But weather forecasters expected record highs of up to 22 to 24 degrees Celsius - a good omen for the outcome for Obama fans.

Mayor Richard Daly told the Chicago Tribune that up to 1 million people could show up, though the campaign was only giving away 65,000 tickets to the secure area closest the stage. Thousands are expected to wait hours for prime spots.

'It's a historic event. If (people) want to be there, they should,' Daley said.