US president-elect Donald Trump has slammed the push for recounts in three states pivotal to his November 8 victory.

The New York billionaire, who charged the election was “rigged” on a daily basis before his victory, called the developing recount effort “a scam” to raise money for Green Party candidate Jill Stein.

Mr Trump had been ignoring Ms Stein’s fight to raise $US7 million ($9.4 million) to revisit vote totals in Wisconsin, Michigan and Pennsylvania.

Wisconsin officials announced late on Friday they are moving forward with the first presidential recount in state history.

“The people have spoken and the election is over,” Mr Trump said.

“We must accept this result and then look to the future.”

Mr Trump’s Democratic rival Hillary Clinton appears to have forced him to address the recount push by formally joining the effort on Saturday.

Ms Clinton’s campaign attorney Marc Elias said: “Because we had not uncovered any actionable evidence of hacking or outside attempts to alter the voting technology, we had not planned to exercise this option ourselves.”

“But now that a recount has been initiated in Wisconsin, we intend to participate in order to ensure the process proceeds in a manner that is fair to all sides.”

The recount process, including an examination by hand of the nearly three million ballots cast in Wisconsin, is expected to begin late next week after Ms Stein’s campaign filed the paperwork, the Elections Commission said.

“The Commission is preparing to move forward with a statewide recount of votes for President of the United States, as requested,” Commission Administrator Michael Haas said in a statement.

The recount must be finished by December 13.

In a Facebook message on Friday, Ms Stein said she had raised at least $US5 million ($A6.7 million) since launching her drive on Wednesday for recounts in Wisconsin, Michigan and Pennsylvania – three battleground states where Republican Trump edged out Ms Clinton by relatively thin margins.

The chance of overturning the result of the election is considered very slim, even if all three states go along with the recount.

The Green Party candidate, who garnered little more than 1 per cent of the nationwide popular vote herself, said she was seeking to verify the integrity of the US voting system, not to undo Mr Trump’s victory.

“This was a hack-riddled election,” she told CNN.

Experts urged extra scrutiny of the three states, Ms Stein said, because they had “unexplained high numbers of undervotes,” and “discrepancies between pre-election polling and the official result.”

The filing deadline for a recount in Pennsylvania is Monday and in Michigan it is Wednesday.

Ms Clinton would need to reverse the result in all three states for the overall election result to change.

Mr Trump beat Ms Clinton in Pennsylvania by 70,010 votes, in Michigan by 10,704 votes and in Wisconsin by 27,257 votes.

– AAP