In Georgia, one of the remaining key states where votes are still being counted, election monitors and US broadcaster CNN are saying that Democrat Joe Biden has taken the lead there for the first time.
Decision Desk puts Biden ahead by a whisker with what it says is about 99% of estimated votes counted.
If Biden takes Georgia, Trump cannot achieve the required 270 Electoral College votes to secure the presidency.
Biden has a slender lead in Nevada and Arizona and is chipping away at Trump’s advantage in Pennsylvania.
Earlier in the night, President Trump again asserted he has won the election, though votes are still being counted.
Trump complained of “tremendous corruption and fraud in the mail-in ballots”, without giving evidence.
Biden urged Americans to remain calm as votes are counted, adding he has “no doubt” he will emerge the winner.