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

As Chicago prepared 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.

Obama was to hold his election night rally at Grant Park along windy Lake Michigan, and unseasonably warm temperatures were expected for the outdoor event. McCain was to hold his election night event in Phoenix, Arizona, the state he has represented in Congress since 1982.

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 as high as 90 per cent possible in some precincts, and new equipment in many states, it could be a long night before the winner is declared.

Election officials in Chicago said they expected about 80 per cent of eligible voters to come out Tuesday, which would be higher than any time since 1972.

'People suddenly are engaged in this election, engaged in the candidates. It's almost like a movement, a renewed interest in the electoral process,' said Langdon Neal, chairman of the Chicago election board.

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.

'We can't afford to slow down, or sit back, or let up, not one minute, not one hour, not one second,' Obama told a cheering crowd in Jacksonville, Florida.

The two candidates touted tried-and-true themes on the final day: McCain hammered Obama as a traditional tax-and-spend liberal politician and Obama continued to tie McCain to the policies of an unpopular President George W Bush.

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 51.2 per cent to McCain's 44.2 per cent on Monday.

McCain remained hopeful and derided pundits who were already predicting victory for Obama. 'They may not know it, but the Mac is back and we're going to win this election,' he told supporters in Blountville, Tennessee.

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.

Obama was set to hold his final rally of the 21-month election campaign in Manassas, Virginia on Monday evening. McCain planned a midnight rally in Prescott, Arizona, as the last stop in a seven- state, 5,940-kilometre tour of the country Monday.

McCain also had a rally set in Grand Junction, Colorado on Tuesday, a rarity for election day. Obama planned to shake hands with voters at polling stations in Indianapolis, Indiana.

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 a 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.