"President Trump is innocent. President Trump did not commit any crimes. The Manhattan District Attorney's office should never have brought this case," Trump lawyer Todd Blanche said.
Blanche spoke shortly after prosecutors laid out their case arguing that Trump broke the law by deceiving voters.
Donald Trump is accused of covering up a hush money payment to porn star Stormy Daniels. (AP PHOTO)
"This case is about a conspiracy and a cover-up, an illegal conspiracy to undermine the integrity of a presidential election, and then the steps that Donald Trump took to conceal that illegal election fraud," prosecutor Matthew Colangelo said.
Colangelo told the jury that they would hear Trump working out the details of the scheme in his own voice on recorded conversations.
Both lawyers made their opening statements in what may be the only one of Trump's four criminal prosecutions to go to trial before his November 5 election rematch with Democratic President Joe Biden.
Colangelo told jurors that Trump engaged in a "catch and kill" conspiracy with his former lawyer Michael Cohen and tabloid publisher David Pecker to cover up unflattering information about Trump and help him defeat Democrat Hillary Clinton.
That included payments to women who said they had sexual encounters with Trump, including a $US130,000 ($A202,000) payment to porn star Stormy Daniels, at a time when he was facing other revelations of sexual misbehaviour, he said.
This may be the only one of Donald Trump's four criminal cases to go to trial before the election. (AP PHOTO)
As the trial opened, Justice Juan Merchan ruled that prosecutors would be able to ask Trump, if he testifies, about two other court cases: one that found he fraudulently misstated the value of his real estate assets, and another that found he defamed writer E Jean Carroll after she accused him of rape.
Merchan also said prosecutors would be able to show jurors a transcript of a tape from the 'Access Hollywood' TV show in which Trump makes vulgar comments about grabbing women's genitals, though jurors will not be allowed to see the tape itself.
Wearing a blue tie and dark blue suit, the Republican presidential candidate stared at the judge and occasionally spoke to his lawyer. A Secret Service agent wearing an earpiece sat directly behind him. Jurors watched Colangelo without expression as he gave his opening statement.
Trump has pleaded not guilty to 34 counts of falsification of business records brought by Manhattan District Attorney Alvin Bragg and denies having had a sexual encounter with Daniels.
The case is seen by many legal experts as the least consequential of the Trump prosecutions. A guilty verdict would not bar him from taking office, but it could hurt his candidacy.
Reuters/Ipsos polling shows half of independent voters and one in four Republicans say they would not vote for Trump if he is convicted of a crime.
Colangelo said Trump falsified cheques, invoices and other documents to disguise his reimbursements to Cohen as legal expenses. Those payments totaled $US420,000 ($A652,000) in all, a sign that the tight-fisted Trump was desperate to cover up his conduct, Colangelo said.
Trump is facing 34 felony counts of falsifying records related to payments made to a porn star. (EPA PHOTO)
He is charged with falsely recording his 2017 reimbursement of Cohen for the Daniels payment as a legal expense in his real estate company's books. Prosecutors say he did so to conceal the fact that Cohen's payment exceeded the $US2700 ($A4000) limit on individual campaign contributions at the time.
Testimony about those payments could help prosecutors establish that Cohen's payment to Daniels was part of a broader pattern.
Prosecutors plan to call at least 20 witnesses total, according to Trump's defence team. The trial could last six to eight weeks.
Before the trial began Monday, Trump called for supporters to protest peacefully at courthouses "all over the Country," but few were on hand to greet him when he arrived at the downtown courthouse. Trump suggested tight security measures were responsible for the sparse turnout, but the streets surrounding the courthouse were open to the public.
"Lower Manhattan surrounding the Courthouse, where I am heading now, is completely CLOSED DOWN. SO UNFAIR!!!" he wrote on social media.
