A New York judge on Thursday rejected Donald Trump's attempts to dismiss charges he covered up hush money payments to a porn star, setting the stage for the first criminal trial ever of a former US president to begin on March 25.

At the same time, Trump's representatives attended a separate hearing in Atlanta, pushing to have the lead prosecutor bringing charges of election fraud and racketeering against Trump disqualified from the case.

They are just two of four criminal cases facing the Republican frontrunner as he campaigns to retake the White House, with his legal teams seeking to push the actual trials until after the November 5 vote.

Trump, who has seized on the media attention of his legal woes to fire up his supporters and denounce Democratic opponent Joe Biden, reiterated his claim that the charges were "just a way of hurting me in the election."

"How can you run for election if you are sitting in a courthouse in Manhattan all day long," he said as he arrived.

Once the hearing got underway, Judge Juan Merchan rejected Trump's request for dismissal or delay, ruling that jury selection would begin as scheduled in late March.

The ex-president's legal team argued he would not receive a fair trial in New York because another Manhattan jury had awarded US$83 million to E. Jean Carroll, a writer whom Trump was found to have sexually assaulted and defamed.

The judge rejected that, as well as arguments by Trump's lawyers that there was too much media coverage for a jury to be unbiased.

"Given all the information I have before me, we are moving ahead to jury selection on March 25," Merchan said.

Trump, who wore a trademark red tie and dark suit, fidgeted in his seat as his lawyer argued with the judge and prosecutors.

The former president faces 34 counts of accounting fraud linked to payments to porn star Stormy Daniels.

Prosecutors say that Trump illegally covered up remittances to his longtime lawyer and aide, Michael Cohen, to reimburse him for payments to bury stories about Trump's alleged extramarital sexual relations with Daniels and a Playboy model.

Trump's lawyers were also representing him in Atlanta, Georgia, where he is accused of conspiracy to overturn the 2020 election, which he lost to Biden.

That hearing seeks to have District Attorney Fani Willis dismissed from the case over an alleged relationship with another prosecutor.

Trump's legal rollercoaster could continue on Friday if, as US media have reported, a ruling is issued in his civil fraud trial, in which he is accused of grossly inflating his property's values.

In that case he risks having to pay up to US$370 million and faces a ban from conducting business in New York state.

And he also faces another possible trial alleging conspiracy to overturn the 2020 election in Washington.

Trump has used the numerous legal cases to fuel his claims of being victimized as he campaigns for a return to the White House.

The hush money case dates to the closing days of the 2016 election when Trump was on the cusp of his shock win as a political outsider against Democratic candidate Hillary Clinton.

A New York grand jury indicted Trump in March 2023 over the payments made to Daniels, whose real name is Stephanie Clifford.

Prosecutors say the money was paid to silence Daniels over claims she had a tryst with Trump in 2006 -- a year after he married Melania Trump.

Late in the campaign, Trump's lawyer Michael Cohen arranged a payment of US$130,000 to Daniels in exchange for her pledge of confidentiality.

Trump for years rejoiced in his reputation as a playboy but he denied the affair with Daniels, which would have occurred just after Melania, his third wife, gave birth. (AFP)