Rav Oelbaum shlita spoke in Queens last year. He quoted the Tzitz Eliezer (and said other contemporary poskim agree) who paskened when asked by someone named “Dr. Abraham” that in a case of clear danger to the person being abused not only may one report it to the authorities, one is “mechuyav” to go straight to the police (it is not relevant that the person will be arrested etc…). If I am not mistaken, this is true even if the ongoing abuse is not life threatening. You can find this talk of Rav Oelbaum Shlita online at torahanytime.com
If I am not mistaken, he quoted R’ Elyashiv Shlita, he should have a refua shlaima bikarov, that in a case of sakana to the abused one must go to the authorities even if it means the child will be put into foster care that is not a frum environment.