By Jonathan Allen and Karen Freifeld

NEW YORK (Reuters) - New York City police have thrown up metal barriers around Trump Tower and blocked roads near Manhattan Criminal Courthouse as they brace for potential protests ahead of Donald Trump's expected surrender to prosecutors on Tuesday.

The former president is due to be arraigned at the courthouse Tuesday afternoon, after his indictment in a grand jury probe over hush money paid to a porn star. He is the first former U.S. president to face criminal charges.

Trump describes the probe as a political witch hunt, and top supporters, including Republican lawmaker Marjorie Taylor Greene, say they will go to New York on Tuesday to protest. The downtown courthouse, home to criminal and supreme courts, will shut down some courtrooms ahead of Trump's expected appearance, a court official said.

The New York Police Department (NYPD) said there were no credible threats to the city.

Some social media users have called for Manhattan District Attorney Alvin Bragg and the jury that indicted Trump to be executed, according to Site Intelligence Group, which monitors online extremism.

After Trump falsely claimed he won the last election, his supporters stormed the U.S. Capitol building on Jan. 6, 2021, sparking a deadly riot.

However, many Trump supporters online have expressed wariness about public demonstrations, even after Trump called for them, concerned they could be arrested.

"(The) department remains ready to respond as needed and will ensure everyone is able to peacefully exercise their rights," the NYPD said in a statement.

Trump is expected to fly to New York on Monday from Florida and spend the night at Trump Tower, before arriving early Tuesday morning at the courthouse, a Trump adviser said.

While the spectacle of the former president facing criminal charges was certain to draw massive media attention, it is not yet clear if his appearance would draw a large number of protesters. While Trump is a native New Yorker, he didn't get many votes in his hometown - 23% of the city voted for him in 2020 and 18% in 2016.

The New York Young Republican Club says it is planning a protest at a park across the street from the courthouse, a demonstration that Greene, one of Trump's staunchest supporters in Congress, says she will attend.

"Protesting is a constitutional right," Greene said on Twitter, adding that she would "protest this unprecedented abuse of our justice system and election interference." She said she rejects anyone who incites or commits violence. Before voting to indict Trump, the grand jury heard evidence about a $130,000 payment to adult film actress Stormy Daniels in the waning days of the 2016 presidential campaign.

Daniels, whose real name is Stephanie Clifford, has said she was paid to keep silent about a sexual encounter she had with Trump in 2006. Trump denies the sexual encounter.

A court official told Reuters that courtrooms on higher floors of the courthouse will be closed at 1 p.m., shortly before Trump's expected 2:15 p.m. (1815 GMT) arraignment.

The official also said many court cases will be adjourned at a building across the street from the courthouse.

The New York case is just one of many probes facing the Republican as he makes another run at the White House. A prosecutor in Georgia is investigating Trump's alleged efforts to overturn his 2020 election defeat in that state.

The U.S. Justice Department is investigating both Trump's actions in the 2020 election and his retention of highly classified documents after departing the White House in 2021.

Joe Tacopina, a Trump lawyer, said on Sunday he expects more details surrounding the arraignment to be resolved on Monday and noted that the Secret Service, which protects former presidents, also has a role to play on Tuesday.

Tacopina said it was unlikely there will be a "perp walk" - perp being shorthand for perpetrator - in which a person who has been charged is paraded in front of the news media, because of security concerns.

"I honestly don't know how this is going to go - hopefully as smoothly as possible - and then we begin the battle to right this wrong," Tacopina told CNN.

Tacopina added that Trump's lawyers will "dissect" the indictment once it is made public and will look at "every potential issue" to challenge. He said he anticipated making a motion to dismiss the charges at some point.

Trump is expected to appear before Justice Juan Merchan, the judge who also presided over a criminal trial last year in which Trump's real estate company was convicted of tax fraud. Trump himself was not charged in that case.

A court official said on Sunday that the judge has asked both sides to submit their positions on whether cameras and video should be allowed in the courtroom and will decide on the issue on Monday.Reporting by Rich McKay in Palm Beach, Florida and Karen Freifeld in New York; Additional reporting by Jonathan Allen, Jeenah Moon and David Dee Delgado in New York, Doina Chiacu in Washington; Writing by Will Dunham Editing by Heather Timmons, Matthew Lewis and Bernadette Baum