"I'm not going to talk about the Trump indictment," he said to multiple shouted questions. "I have no comment on Trump."
The White House has released no formal statement since the revelation on Thursday that Trump would become the first ever former president to face criminal charges, over a hush money payment to a porn star during the 2016 election.
Biden's administration, seeking to avoid any perception of influencing the justice system, will likely remain "quiet for as long as they can," former press secretary Jen Psaki said on MSNBC.
Trump quickly claimed the indictment was "political persecution and election interference," and accused Manhattan District Attorney Alvin Bragg of "doing Joe Biden's dirty work."
Other top Republicans similarly expressed outrage at Bragg, an elected Democrat, with House Speaker Kevin McCarthy pledging to hold him to account over an "unprecedented abuse of power."
Psaki advised the White House to "keep your head down" and don't "feed into the politics of this."
Until now, her successor at the White House press room podium, Karine Jean-Pierre, has remained silent on the legal proceedings against Trump, using as cover a law that prohibits government officials from discussing future elections.
Biden's Democratic Party will however be broadly content with the dual-image split screen that could soon come: Biden touring the country touting economic programs, Trump appearing in court.
After Mississippi, Biden will travel to his home in Delaware, where he spends most weekends.
But on Monday, he plans to travel to the northern city of Minneapolis, where the White House says he will "discuss how his economic agenda has led to the strongest job growth in history."
A day later, Trump is expected to arrive in New York for his arraignment, and to have his finger prints and a mugshot taken.
The indictment of the Republican -- which in no way prohibits him from campaigning -- may have a mobilizing effect in his own camp, and fuel fundraising efforts.
Senior members of his party flocked to support Trump on Thursday, including the man believed to be his biggest rival for the Republican nomination, Florida Governor Ron DeSantis.
Biden, 80, believes that in a head-to-head race with 76-year-old Trump, the Democrat will once again emerge victorious, and that his age will be less of a handicap.
"In the next election, I'd be very fortunate if I had that same man running against me," Biden said recently of Trump, whom the Democrat narrowly defeated in 2016.
A recent Marquette Law School poll showed Biden neck and neck with his former opponent, at 38 percent each.
The race will likely swing once again on the key voting bloc of independents and undecideds.
To sway those groups, Biden has been honing arguments on the cost of living, defending health insurance reforms, and protecting social programs -- which, he argues, the Republicans want to dismantle.
But polling shows that Americans remain concerned about the economy, with a Quinnipiac University poll on Thursday saying that 68 percent of Americans are worried about their post-retirement standard of living.
In recent months, Biden has slowed, if not fully abandoned, remarking directly on his predecessor, like he did last September in a major speech in Philadelphia.
Biden, in a rare attack on Trump, accused him of feeding an "an extremism that threatens the very foundations of our republic."
© Agence France-Presse