With just over a week to go before Americans head to the polls, U.S. presidential nominees Barack Obama and John McCain began making their closing arguments on Monday.

In Ohio, where Obama is facing a tight neck-and-neck race with his Republican rival, the Democratic senator told voters to continue their fight to change Washington politics.

"We are one week away from changing America," he told supporters in the industrial town of Canton.

"Now, after 21 months and three debates, Sen. McCain still has not been able to tell the American people a single major thing he would do differently than George Bush when it comes to the economy. Not one thing."

Ohio, an important battleground state where Bush eked out a victory in 2004, remains a virtual tie, but in many state polls Obama appears to have a significant lead nationally. Some national estimates have had him up by double digits, although most analysts say he is likely ahead by about six points.

The significant national lead -- and his gains in traditionally red states such as North Carolina, Virginia, and Florida -- has some Democrats predicting a landslide victory come November 4.

Such exuberance has forced Obama on several occasions to tell his supporters not to rest on their laurels by becoming complacent. On Monday, he said that message is especially important in the closing days of the campaign.

"We cannot afford to slow down or sit back. We cannot let up for one day or one minute or one second in this last week. Not now. Not when there's so much at stake," he said, as the crowd roared with approval.

Obama emphasized themes he has repeated throughout his campaign and in his three debates with McCain. He promised tax breaks for the middle class and tax help for American companies that don't ship jobs abroad.

He also told voters an Obama administration will introduce policies that will help them afford college for their kids and protect their jobs in uncertain economic times.

Ohio has seen almost 250,000 factory jobs disappear since 2000. The state's unemployment is well above the national average (6.1 per cent), hovering above 7 per cent.

"At a moment like this, the last thing we can afford is four more years of the tired, worn out old theories that say we should give more to billionaires and big corporations and hope that prosperity trickles down on everybody else," Obama said.

McCain also campaigned in Ohio on Monday, where he continued to separate himself from the policies of U.S. President George Bush.

"We both disagree with President Bush on economic policies," McCain said.

"My approach is to get spending under control. The difference between us is he (Obama) thinks taxes have been too low, and I think that spending has been too high."

McCain also promised to create millions of jobs through tax cuts "that spur economic growth."

Both Obama and McCain will also head to Pennsylvania on Monday. Polls there show Obama well ahead, but Republicans say their internal polls show the race to be tighter than the double-digit spread indicated by other surveys. Together Ohio and Pennsylvania have 41 electoral votes. A candidate needs at least 270 electoral votes two win the election.