Donald Trump says he would have won US popular vote if not for illegal voting

The allegation, made without evidence, comes as Democratic rival Hillary Clinton's lead in the popular vote over Trump has surpassed 2 million votes and is expected to grow to more than 2.5 million as ballots in populous states such as California continue to be tallied.

Clinton's legal team said on Saturday it had agreed to participate in a recount of Wisconsin votes after the state's election board approved the effort requested by Green Party candidate Jill Stein, which Trump has called "ridiculous."

"In addition to winning the Electoral College in a landslide, I won the popular vote if you deduct the millions of people who voted illegally," Trump tweeted as reporters waited for him to leave his Mar-a-Lago golf resort in Florida to fly back to his residence in New York City.

The US presidential race is decided by the Electoral College, based on a tally of wins from the state-by-state contests, rather than by the national vote. Trump has surpassed the 270 electoral votes needed to win the White House. The Electoral College results are expected to be finalized on December 19.

Trump added he would have won the "so-called popular vote ... easily and convincingly" if the US election was determined that way instead of by the Electoral College. Before the election, Trump made unsubstantiated allegations that the results of the election might be "rigged" against him.

Since the vote, Trump's message has alternated between appealing for unity and railing against his opponents and the media.

In a video message released ahead of the US Thanksgiving holiday on Thursday, Trump said he hoped it would be a time for Americans "to begin to heal our divisions" following a "long and bruising political campaign."

Trump has derided the fundraising effort by Stein to launch recounts in Wisconsin, Michigan and Pennsylvania as a "scam." Those states had voted Democratic in recent presidential elections but all broke narrowly for the Republican Trump in this month's election. The recounts are not expected to change the results of the election.

Stein, who won about 1 per cent of the national vote, has said she wants a recount to guarantee the integrity of the US voting system, a push that came after some experts raised the possibility that hacks could have affected the results.

Democratic President Barack Obama's administration has said there is no evidence of electoral tampering, but experts have said that the only way to verify the results are accurate is to conduct a recount.

Trump and Vice President-elect Mike Pence have a series of meetings in New York on Monday to interview potential Cabinet members and other advisers. Trump takes office on January 20.