Terror erupted moments after that 3-year-old boy fell in Harambe the gorilla’s enclosure at the Cincinnati Zoo … and we just got the 911 call.

In the emergency call — released by cops — you can hear Michelle Gregg‘s panicked conversation with dispatch … screaming that her son had just fallen into the gorilla pen.

Michelle tells her son to “be calm,” as she exclaims, “He’s dragging my son. I can’t watch this.”

As we previously reported … cops are reviewing the incident to see if any fault lies with the boy’s parents.