Vice President and Democratic candidate for president Kamala Harris released a video of her phoning up supporters to ask if they'd voted yet, as the US election continued across the country on Tuesday.

"I just wanted to call you, check in and make sure you know where you can go vote today if you haven't already. Have you voted yet?" she asked one voter, Jennifer, who replied "Oh my gosh yeah!"

Jennifer then told Harris she had a 'future voter', eight-year-old Sage, who wanted a word.

"It's Kamala Harris. I can't wait for you to grow 10 years more," she told the youngster. "And Sage, I can tell you're really smart and you're working really hard and I'm counting on you OK? Because you are still a leader at every age that you are, at eight years old, that's a serious leadership and responsibility."

Voters are going to the polls across the United States on Tuesday, November 5, with the race between Harris and Republican former president Donald Trump reported to be too close to call.

The election, held under the electoral college system, requires candidates to pick up 'electoral votes, with the number assigned to each state equal to the number of senators (2) and house representatives - which are based on population. All except Maine and Nebraska operate a 'winner takes all' system based on the state's popular vote, while 270 of the 538 in total are needed to win.

The race is set to come down to just a handful of 'battleground states'; Pennsylvania, Wisconsin, North Carolina, Georgia, Michigan, Arizona and Nevada.

All 435 seats in the House of Representatives and 34 of 100 Senate seats are also up for election. There are also 13 state and territorial governorships and many other state and locals elections too.