US President Joe Biden said on Friday that it was "dangerous" for people to question the integrity of the guilty verdict in Donald Trump's hush money jury trial.

In his first public comments since a New York jury on Thursday found Trump guilty on 34 counts over a payment to silence an adult film star ahead of the 2016 election, Biden, a Democrat, struck out hard at Trump and other Republicans who have criticised the verdict.

"Donald Trump was given every opportunity to defend himself." Biden said. He noted that the case against Trump in New York was brought by the state, that it was not a federal case, and that the verdict was delivered by "a jury of 12 citizens, 12 Americans, 12 people like you."

The US justice system has endured for nearly 250 years, Biden said, and he criticised Trump and his supporters for attempting to tear it down with false allegations.

"It's reckless, it's dangerous, it's irresponsible for anyone to say this was rigged just because they don't like the verdict," Biden said.

In rambling remarks earlier on Friday at the Trump Tower lobby in Manhattan, Trump repeated his complaints that the trial was an attempt to hobble his comeback White House bid and said it showed that no American was safe from politically motivated prosecution.

"If they can do this to me, they can do this to anyone," Trump said in an unscripted 33-minute speech.

Thursday's guilty verdict catapults the United States into unexplored territory ahead of the November 5 vote, when Trump, 77, will try to win back the White House from Biden, 81. (Reuters)