The election will decide who will hold the country's highest office and end a campaign marked by ugly rhetoric and personal attacks, all of which helped expose a deep and bitter divide in the electorate.
Voters are choosing between Democrat Hillary Clinton, the favourite going into election day, or Republican Donald Trump.
Clinton's vice presidential candidate Tim Kaine was shown on CNN casting his vote as the polls opened.
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Both campaigns kept up the pressure until the end. Clinton's campaign ticked down the minutes until the start of the polls with calls to vote and to "build bridges, not walls," a dig at Trump's promise to build a wall with Mexico to keep out illegal immigrants.
Trump's Twitter feed was more sedate, but highlighted his final round of campaign stops ahead of the start of voting.
"Today we are going to win the great state of MICHIGAN and we are going to WIN back the White House!" read the most recent message.
Polling locations will continue to open across the US all the way to Hawaii, the state farthest to the west. Millions of voters already have cast their ballots in early voting, which is offered in 34 states and in Washington.
Here's a list of which states close polls and when in Australian Eastern Daylight Time.
0900 Wednesday AEDT : Parts of Indiana, Kentucky
1000 AEDT - most of Florida; Georgia, South Carolina, Vermont, Virginia,
parts of New Hampshire, rest of Kentucky and Indiana
1030 AEDT: Ohio, North Carolina, West Virginia
1100 AEDT : Alabama, Connecticut, Delaware, DC, Illinois, Kansas, Maine,
Maryland, Massachusetts, Michigan, Mississippi, Missouri, New Jersey,
Oklahoma, Pennsylvania, Rhode Island, Tennessee, Texas, first parts
of North and South Dakota, latter parts of Florida and New Hampshire.
1130 AEDT: Arkansas
1200 AEDT: Arizona, Colorado, Louisiana, Minnesota, Nebraska, New
Mexico, Wisconsin, Wyoming, second parts of North and South Dakota
1300 AEDT: Most of Idaho; Iowa, Montana, Nevada, Utah
1400 AEDT: California, Oregon, Washington, rest of Idaho
1500 AEDT Wednesday: Alaska
1600 AEDT: Hawaii
