Supporters of both candidates have started to gather to await the official declaration of the results.
The first polls have closed and first projected results are in, as a ground-breaking US presidential election nears its climax.
Tens of millions of people across the United States have been going to the polls to elect a new president.
Several key states are reporting a heavy turnout. A total of 130 million Americans are expected to vote.
If figures prove correct the resulting turnout could be the highest in any election since 1960.
Libraries, churches, schools and some more unusual facilities have become polling stations in order to handle the huge numbers of voters.
The Ruby polling station is located in a one-room building that dates back to the 1880s, and has been the polling place for voters in rural Seward County, Nebraska, for over 100 years.
Election officials in some states are anticipating that as many as 80% of eligible voters will turn up to cast their ballots.
Record numbers of young people and people from minority backgrounds are expected take part in the election this year.
Officials say anyone waiting in a queue when polls close will still be allowed to cast their ballot.
Democratic candidate Barack Obama cast his vote in Chicago, Illinois, where he is a senator, with his wife Michelle.
Meanwhile, Republican nominee John McCain and his wife Cindy turned in their ballots in Phoenix, Arizona.
However, McCain continued to court voters with two final campaign stops in Colorado and New Mexico.
Problems with polling have been expected as the US system is set up for what is usually a low turnout in presidential elections.
And some districts in New Jersey and Virginia have already reported problems with electronic voting machines.
Mr Obama has been leading opinion polls - but Mr McCain is pinning his hopes on a last-minute resurgence.