Protesters have gathered on the streets of the United States as President Donald Trump's campaign filed lawsuits to contest the vote count, with the election outcome still unknown.
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Democratic challenger Joe Biden defeated Trump in two key northern states of Wisconsin and Michigan.
But the swing states of Pennsylvania, Nevada, Georgia and Arizona remained unclaimed late Wednesday night in the United States with a long, tense wait ahead.
As of 2.30pm on Thursday (AEDT), Biden had 253 electoral votes and Trump had 214.
It requires 270 electoral votes to become president.
Wisconsin and Michigan have flipped to the Democrats, both key swing states which had been claimed by Trump in 2016.
As his path to victory narrows, Trump's campaign has filed lawsuits to contest the vote count in Pennsylvania, Michigan and Georgia.
Protestors lined the streets of Pennsylvania, a block away from where votes continue to be counted, rallying against Trump's call for a recount.
Trump has taken the lead in Pennsylvania by more than 200,000 votes, with 12 per cent of the vote still to be counted.
Biden has inched ahead narrowly in Nevada and Arizona, with 86 and 82 per cent of the vote counted respectively.
Nevada will not be updating voting data until midday Thursday in the US, but numbers are expected from Arizona and Georgia within hours.
Biden held a 2.8 per cent lead in Arizona, and Trump led Georgia by 0.7 per cent as of Thursday afternoon (AEDT).
Biden said he was confident the Democrats could take Pennsylvania and were "on track" to take the White House.
"Here, the people rule. Power can't be taken or asserted. It flows from the people. It is their will that determines who will be the president of the United States, and their will alone," he said.
"It's clear that we're winning enough states to reach 270 electoral votes needed to win the presidency.
"I'm not here to declare that we've won. But I am here to report, when the counting is finished, we believe we will be the winners."
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Trump spoke at the White House about 2.30am, saying he would go to the Supreme Court to try to stop "all voting".
"This is a major fraud on our nation," Trump said.
"We don't want them to find any ballots at 4 o'clock in the morning and add them to the list."
In the US Senate, undecided seats are keeping both sides from claiming control of the upper house of the US legislature with counting continuing.
Democrats already control the House of Representatives.
