The first handful of votes have been cast on US election day as part of one town's tradition of being "first in the nation".

Polls open elsewhere later tonight, with most of the action for us taking place on Wednesday, November 9, Australian time.

Otherwise, here are the key times you need to know and the states you need to watch as we await a winner:

Tuesday, 4pm AEDT

At midnight local time, eight ballots were cast in Dixville Notch, New Hampshire.

The results were: four votes for Hillary Clinton, two for Donald Trump, one for Libertarian candidate Gary Johnson, and one for 2012 Republican candidate Mitt Romney (via a write-in).

Tuesday, 10pm AEDT

Polls open in some states on the east coast.

Depending on the state, polling booths will open between 6am or 7am local time and close between 7pm or 8pm. (If you're in line when polls close, you still get to vote.)

Fun fact: there are six different time zones across the United States, but just to make things nice and complex there are 13 states operating with split time zones.

The point is, most voting will take place overnight Tuesday, Australian time.

Wednesday, 11am AEDT

Polling stations will start to close in eastern states.

Once the polls have closed, there will be a projection for each state based on opinion polls taken throughout the day. They are a good indication of the results but not always correct.

The key results to watch out for at this time are from swing states Florida, New Hampshire and Virginia.

Wednesday, 11:30am AEDT

Polls close in two more battleground states — North Carolina and Ohio. Mr Trump's best chance at victory is seen as more or less requiring a win from either Ohio or Florida, if not both.

In other words, this is when we might get an indication of how well Mr Trump is faring.

Wednesday, 12pm AEDT

Polls close in 18 states, the most important being Pennsylvania.

This is also when the final polls close in Florida (it's one of the states with a split time zone), so we might not get those projections until this time.

Wednesday, 1pm AEDT

Polls close in 10 states, including Wisconsin and swing state Colorado.

While Mrs Clinton is considered the favourite to win Wisconsin, a Trump upset there would point to a tight race across the board.

The final polls close at this time in Texas which has been solidly Republican, but which Democrats were hoping an increased migrant turnout might turn in their favour. If that happens, it would be a huge result.

Wednesday, 2pm AEDT

Voting ends in swing states Nevada and Iowa and three others seen as safe Republican territory.

If Mr Trump doesn't win Iowa, he's seen as being pretty much done. Although by this time, we should have a decent idea of how the night has played out.

Wednesday, 3pm AEDT

Voting closes in states on the west coast, including California, which is very much safe ground for Mrs Clinton.

Polls close in Alaska at 5pm AEDT, but it is a small state so it is unlikely to affect the outcome.

When will the winner be named?

The close of the polls on the west coast (i.e. 3pm AEDT) will be the first opportunity for the election to be "called". The US television networks and cable channels nowadays generally agree to wait until this time to declare a winner so as not to affect voting turnout in those states.

The magic number is 270 — that's the number needed for a majority in the electoral college, where each state (plus Washington DC) is awarded a certain number of electoral college votes based roughly on size and population.

The first candidate to reach 270 wins, and swing states dictate the outcome.

Like in Australia, the losing candidate will usually call the winner to concede defeat once that number has been reached.

Where will Clinton and Trump be?

Mrs Clinton and Mr Trump haven't confirmed when or where they will cast their ballot, but they are both expected to do so somewhere in New York.

Mrs Clinton's 'Hillary for America Election Night Event' will start at 6pm at the Jacob K. Javits Convention Centre in New York.

The 'Donald J Trump Victory Party' will start at 6.30pm at the New York Hilton Midtown.

So, what if we don't get a result on the night?

This happened in 2000 in the election between president George W. Bush and former vice-president Al Gore.

Mr Bush won the presidency after a recount in Florida, via a challenge in the US Supreme Court.

Barack Obama remains president until January 2017, so there's plenty of time for recounts if need be.

What if they tie?

There is a possibility that two candidates will get 269 electoral college votes. It's also possible no candidate will reach the 270 target.

But don't worry, America's constitution covers these scenarios.

If no single candidate receives an electoral college majority, the House of Representatives has to decide from the candidates with the top three electoral vote counts.

Each state delegation has to make the decision, not each representative. Current numbers favour the Republicans, but the vote wouldn't take place until January, when the next Congress is sworn in.

If there is still no winner, the job goes to the vice-president-elect. However it will be up to the Senate to vote on which vice-presidential candidate is named vice-president-elect.

If we still have no winner, the presidency goes to the Speaker of the House. That is Republican Paul Ryan.

When will the winner be given the keys to the White House?

Not for a while.

The new president and vice-president will be sworn in at noon on January 20, Washington DC time.

That might seem like a long wait, but up until 1937 presidents weren't usually sworn in until March because it took so long to count and report the results.

And if after all that, you fear US election withdrawal, don't worry — after that it'll be less than two years until the mid-terms!

source : abc