Twelve New York jurors began deliberating Wednesday on whether to convict Donald Trump in the first-ever criminal trial of a former US president -- with their decision potentially upending the November election in which the Republican seeks a return to power.

After weeks of testimony from more than 20 witnesses, the piercing glare of the legal spotlight shifted to the jury, whose identities have been kept secret for their own protection amid soaring political tensions across the United States.

After receiving final instructions from the judge, the jury retired to consider a verdict that -- whichever way it goes -- will have an outsized impact on Trump, and the country as a whole.

No time limit is placed on their deliberations, but an acquittal or conviction would require unanimity. If just one juror refuses to join the others, the judge would have to declare a mistrial.

Trump is accused of falsifying business records to reimburse a $130,000 payment to silence adult film star Stormy Daniels, when her account of an alleged sexual encounter could have imperilled his 2016 presidential campaign. Prosecutors say the fraud was motivated by a plot to prevent voters from knowing about his behaviour.

If Trump is found guilty, the political repercussions would far outweigh the seriousness of the charges as, barely five months before the presidential election, the candidate would also become a convicted criminal.

Trump fired off a characteristically angry, all-caps message on his Truth Social app, complaining about a "KANGAROO COURT!" and a "CORRUPT AND CONFLICTED JUDGE."

In a full day of closing arguments on Tuesday, his defence team insisted the evidence for a conviction simply did not exist, while the prosecution countered that it was voluminous and inescapable.

"The defendant's intent to defraud could not be any clearer," said prosecutor Joshua Steinglass, urging the jurors to use their "common sense" and return a guilty verdict.

If convicted, Trump faces up to four years in prison on each of 34 counts, but legal experts say that as a first-time offender he is unlikely to get jail time.

A conviction would not bar him from the November ballot and he would almost certainly appeal. In the case of a mistrial, prosecutors could seek a new trial.

- 'Hatred for Trump' -

Trump, who was required to attend every day of the trial and will also have to be present while the jury deliberates, chose not to testify in his defence.

However, he used his trips to court to claim the trial is a Democratic ploy to keep him off the campaign trail.

Polls show Trump neck and neck against President Joe Biden, and the verdict will inflame passions as the White House race intensifies.

In addition to the New York case, Trump has been indicted in Washington and Georgia on charges of conspiring to overturn the results of the 2020 election.

He also faces charges in Florida of hoarding huge quantities of classified documents after leaving the White House.

The New York case is the only one likely to come to trial by election day.