State TV reported that the girl known only as "Belen" is 14 weeks pregnant. Police arrested her mother's partner who confessed to abusing the fifth grader. Doctors say her life and that of the fetus are at high risk. But ending the pregnancy is not an option.
Chile allowed abortions for medical reasons until they were outlawed in 1973 by Gen. Augusto Pinochet's dictatorship. The current government of conservative President Sebastian Pinera has opposed any loosening of the prohibition.
Many Chileans were venting outrage on social media Friday. Some have started an online campaign to demand legalization of abortion in cases of rape or health risks for mother.
Chile's Senate rejected three bills last year that would have eased the absolute ban on abortions.
One of the bills would have permitted abortion when two doctors said it was needed because of risks to a mother's life or other medical reasons, such as a fetus with low chances of survival. Another of the measures rejected would have allowed abortion in the event of rape.