A member of Alternative for Germany (AfD) attacked the teenager, Benigna Munsi, who will open the city's Christmas market on November 29, the BBC report said.
The teen was born in Nuremberg to an Indian father and a German mother.
"You would laugh about it if you didn't know these guys are serious, but you could cry about this level of misanthropy," Mayor Ulrich Maly said in a presser on Sunday.
While he said there had been "idiotic comments" about previous Christ Child actors' appearances, this attack had an "openly racist connotation".
A now-deleted Facebook post by an AfD district branch said that German people were being eradicated like Native Americans.
"Nuremberg has a new Christ Child. One day, we're going to go the way of the Ind," it read.
Another AFD member meanwhile provoked further criticism for writing online that the teenager's "foreign" nose was a "slap in the face to friends of tradition".
But leader of the state of Bavaria, Markus Soder, said the state would not tolerate the comments, while Bavaria's interior minister Joachim Herrmann said they were witnessing "the malicious grimace of racism".
City authorities unanimously chose Munsi as the Christ Child on October 30, the BBC reported.
Every previous actor playing the infant Jesus has been white.
The 17-year-old described herself as "mega-happy" after her selection, while Nuremberg's city council said her "fresh, warm, empathetic and easygoing manner" impressed the jury.
Her key role during her two-year tenure will be to open the city's famous Christmas market on November 29, but she will also tour local towns, schools and retirement homes.
( With inputs from IANS )