The woman went down the river and under the bridge where she was submerged under the water.
She went over the falls at the bottom and then popped up and was seen swimming around.
The man rang 111 and instructed the operator to dispatch a jet boat to the bottom of the falls. He also climbed down the bank to try to reach her, but Hukafalls Jet arrived and plucked her from the water.
The Huka Falls area was as busy as it normally is on weekends, with the carpark two-thirds full, 20 or so people on the bridge and more in the surrounding areas.
The Waikato River was running at a low flow of about 60 cubic metres per second at the time.
A police media spokeswoman said she had no information on the woman's injuries, only that she was being checked by ambulance staff.