The incident happened on Somerset Street at 8:30 a.m. Monday.
Police say the two girls, who are both under age 16, were on the second floor of the home when the man broke in.
He allegedly went into a bedroom, sexually assaulted one girl, and then engaged in lewd conduct with the other.
Police say one of the girls went to call for help, and the man ran away.
Police released a sketch of the man, who is said to be Hispanic, about 40 years old, with a thick moustache.
He was wearing a black cap (with the letters AB in white lettering on the back), a silver wristwatch on his left wrist, a white T-shirt, black pants, and black sneakers.
Anyone with information on the assault, or who may be able to identify the man in the sketch, is asked to call Detective Dominguez at (732) 745-5200, or Investigator Kelly at (732) 745-3600.