WASHINGTON (AFP) - US President Donald Trump alleged on Wednesday (Nov 4) that there had been "surprise ballot dumps" in states where he had been leading Democrat Joe Biden in the race for the White House.

"Last night I was leading, often solidly, in many key States, in almost all instances Democrat run & controlled," Trump tweeted.

"Then, one by one, they started to magically disappear as surprise ballot dumps were counted."

Trump did not offer any evidence for his allegation of "ballot dumps" and there have been no reports of any irregularities.

Twitter labelled his tweet as "misleading", as it had done with an earlier message from the president. Users were able to read the tweets after clicking through a warning that "some or all of the content shared in this Tweet is disputed and might be misleading."

The leads in numerous states have shifted back-and-forth between the candidates as votes are counted.

Trump, who overnight prematurely declared himself the winner of Tuesday's election, has spent months denouncing mail-in ballots, making unsubstantiated claims that they are liable to fraud.

"How come every time they count Mail-In ballot dumps they are so devastating in their percentage and power of destruction?" he tweeted on Wednesday.

The usage of mail-in ballots soared this election amid the coronavirus pandemic and the US Elections Project said a record 65.2 million Americans voted by mail.

For live updates and results, follow our US election live coverage.