Mr Biden has 243 Electoral College votes, giving him the edge in the race to accumulate the 270 needed to win the White House. Mr Trump has 214.
In the US election, voters decide state-level contests rather than a single, national one. Each US state gets a certain number of electoral college votes partly based on its population, with a total of 538 up for grabs.
If Mr Trump does lose Wisconsin (10 electoral college votes), he must win Georgia (16 votes), North Carolina (15), Pennsylvania (20) and either Arizona (11) or Nevada (6) to prevail.
Officials in Georgia said they would keep going all night until counting was finished, but as of midnight local time (05:00 GMT) they reported that there were still about 90,000 votes to count. At that time President Trump was leading by some 31,000 votes.
In Arizona, Mr Biden was leading by about 80,000 votes, with further results expected on Thursday. CBS has categorised it as a “likely” win for the Democrat. Supporters of Mr Trump gathered outside a vote counting centre in Maricopa County (which includes Phoenix, the largest city in the state), where officials vowed to “continue our job”.
An update on the count in Nevada – where the candidates were neck-and-neck – is not expected until Thursday at 17:00 GMT (09:00 local time), while in Philadelphia, counting is not expected to finish for several days.
