Manhattan District Attorney Alvin Bragg's office said in a statement that it has contacted former President Donald Trump's attorney "to coordinate his surrender" for arraignment on a state Supreme Court indictment, noting that it remains under seal.

"Guidance will be provided when the arraignment date is selected," the office said.

In the wake of the indictment, all officers with the New York Police Department have been ordered to show up in uniform Friday morning for deployments around New York City, police sources told ABC News.

There are no credible threats, according to the mayor's office.

The indictment of Donald Trump marks an unprecedented development in the country's history -- the first time a former president has ever faced criminal charges.

Historians say that not since Richard Nixon had there been the real prospect of a commander-in-chief being formally accused of a crime, though Nixon avoided that fate after being pardoned by successor Gerald Ford.

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-ABC News' Tal Axelrod

Republican National Committee Chairwoman Ronna McDaniel called the indictment "a blatant abuse of power from a DA focused on political vengeance."

"When our justice system is weaponized as a political tool, it endangers all of us," she tweeted.

Criminal prosecution proceedings typically start with an arrest and a court appearance, but legal experts say that on many occasions, especially in white collar crimes, suspects aren't hit with charges or a visit from an officer until long after an official investigation is underway.

Typically, if a crime is being investigated, law enforcement agents will make an arrest, file initial charges and bring a suspect to be arraigned in court, Vincent Southerland, an assistant professor of clinical law and the director of the criminal defense and reentry clinic at NYU School of Law, told ABC News.

After this arraignment, prosecutors would impanel a grand jury for a formal criminal indictment. Southerland, who has been practicing law in New York state for 19 years, said this process includes giving the jury evidence, possible testimony and other exhibits before they can officially charge a person with felonies.

A Manhattan grand jury is currently investigating Trump's possible role in the hush payment to adult film actress Stormy Daniels. The former president has denied any wrongdoing and having an affair with Daniels. His attorneys have framed the funds as a response to an extortion plot.

-ABC News' Ivan Pereira