Dozens of threats were directed at Merchan and his chamber, the sources told without specifying the time frame for the threats.
Bragg, who presented charges against Trump earlier in the week, and top officials of his office have also been receiving numerous threats in the form of calls, emails and letters, according to other sources.
The New York police assigned to the Manhattan DA's office have increased security of Bragg and his staffers as a precautionary measure, with court officers taking similar action to provide necessary security for the judge, NBC also reported.
On Tuesday, Trump made his first appearance in court to be arraigned after a Manhattan grand jury last week indicted him on 34 counts of falsifying business records in the first degree before and after the 2016 presidential elections.
Charges against Trump are connected with his alleged involvement in a $130,000 hush money payment and subsequent cover-up involving a purported affair with pornography actress Stormy Daniels, among others. Trump pleaded not guilty to the charges during his arraignment.