A Colorado woman is facing an attempted murder charge after allegedly cutting a baby out of a pregnant woman's stomach.

A pregnant US woman had her seven-month-old baby cut from her abdomen by a woman who had posted an ad on Craigslist for infant clothes, police say.

The 34-year-old suspect - who then took the dead baby to a local hospital, claiming she had had a miscarriage - was due in court a day after the grisly incident in the small Colorado town of Longmont, north of Denver.

The 26-year-old victim was operated on and survived after the attack on Wednesday.

Police on Thursday released a harrowing 911 emergency call in which the victim begged for help.

"Officers entered the home and located a female who had been beaten and stabbed in the stomach," local police spokesman Jeff Satur said.

"It was later learned, the female was pregnant and her baby had been removed. The victim was transported to the LongmontUnitedHospital where she underwent surgery and is expected to recover."

The suspect "was located at the LongmontUnitedHospital with a deceased baby, reporting a miscarriage. The suspect and victim were not known to each other prior to this incident".

Satur said the suspect was due in court Thursday afternoon, facing a charge of attempted first degree murder.

Craigslist is a free online classified listings service.