UPDATE - Millions of Americans voting in tight race between Harris and Trump as polls open nationwide

UPDATES HEADLINE, LEDE; ADDS ADDITIONAL INFORMATION

By Michael Hernandez

WASHINGTON (AA) - Millions of Americans are casting their ballots Tuesday as polling stations open across the US with the future of the American presidency coming down to a nail-biter race between Democratic candidate Kamala Harris and Republican nominee Donald Trump.

The first polls began to open at 5 a.m. Eastern Time (1000GMT) in some parts of Vermont, but the first major wave of openings happened at 6 a.m. Eastern (1100GMT) with stations opening their doors in Connecticut, New Jersey, New York, and Virginia, as well as parts of Kentucky and Maine.

North Carolina, Ohio, and West Virginia opened at 6.30 a.m. Eastern Time (1130GMT).

As of noon Eastern Time (1700GMT) all polls across the US opened, with Hawaii being the last. Polls closing will begin in some states as early as 5 p.m. Eastern (1000GMT Wednesday), with Alaska remaining open the longest, until 1 a.m. Eastern Time Wednesday (0600GMT).

According to media reports, voting in Cambria County, Pennsylvania have been extended for an extra two hours due to malfunction of the electronic voting system software.

Anyone who is in line at the time polls officially close will be allowed to cast their ballots, however, meaning stations are likely to remain open beyond their official closure time as long as voters remain in line.

Nearly 83 million people cast early ballots in this year's election cycle by mail or in-person voting, according to data from the University of Florida's Election Lab. That is far short of the over 101 million who did so in 2020, when the US was in the throes of the COVID-19 pandemic.

As of Monday, Trump and Harris were locked in a virtual dead heat nationally, with Harris just +0.1% ahead with 48.7% and Trump at 48.6%, according to a compilation of polling compiled by the RealClearPolitics website.

-Swing states likely to decide race

But rather than national support, the race is all but certain to come down to seven key battleground states – Arizona, Georgia, Michigan, Nevada, Pennsylvania, North Carolina, and Wisconsin – where the nominees are facing similarly narrow contests with spreads well within the polls' margins of error.

Trump's lead is greatest in Arizona, where he is up by 2.8%, followed by Georgia (+1.3%), North Carolina (+1.2%), Nevada (+.06%), and Pennsylvania (+0.4%). Harris continues to lead in Michigan (+0.5%) and Wisconsin (+0.4%).

The polls have margins of error of between roughly 3%-5%.

Both candidates spent the final week before the election campaigning hard in the states, with Harris visiting Pennsylvania for a series of rallies in multiple cities Monday and Trump spending the day there before a late-night rally in Grand Rapids, Michigan.

It is highly unlikely that major media organizations will declare a victor Tuesday night, as had been the norm up until 2020, due to the closeness of the races in the battleground states.

Battleground states are pivotal because the US does not directly elect its presidents. Instead, the process plays out via the Electoral College, where 538 representatives cast their ballots in line with their states’ outcomes.

Either candidate needs to secure 270 Electoral College votes to claim victory. Electors are allocated to states based on their population, and most states give all of their electors to whichever candidate wins the state in the general vote.

The winner-take-all model is not followed in Nebraska and Maine, however, which instead allocate their votes based on the outcome in congressional districts, as well as the state’s popular vote winner.

-Control of Congress up for grabs

Further down the ballot, voters will determine the composition of the next US Congress.

In the Senate, 34 seats are up for election. Senators are elected to six-year terms and one-third are elected every two years. Roughly four of the races are considered toss-ups, including contests in Michigan, Ohio, Pennsylvania, and Wisconsin, which are currently held by Democrats.

Republicans are slightly favored to win numerical control of the Senate, but whoever emerges victorious will be left to navigate a precarious razor-thin majority. In the 100-seat Senate, due to procedural rules, parties often need 60 rather than just 50 votes to pass legislation.

All 435 seats in the House of Representatives are up for election, and as with the Senate, most forecasts have the chamber near-evenly split. Just a couple of dozen competitive elections will determine whether Republicans or Democrats will control the House.

At the state and local levels, voters will decide on a range of initiatives and races, from school boards to state-level ballot measures that can hold the weight of law. A total of 11 governor’s races across the nation are being contested.

*Merve Aydogan contributed to this story.