A group of Sacred Heart Girls' College students were giggling about how fast a woman was zooming down a hill on her mobility scooter before she flew off it and into the river, prompting the girls to instantly move into rescue mode and save her.

The group of girls were heading back to school after having a PE class at Pirana Park on the banks of the Waikato River today when they saw the 58-year-old plunge 20 metres over a bank into the river near the old Waipa Delta pier about 1.30pm.

"We kind of just froze for a bit, but then we ran down and we had to go down another hill and we just started running to the bushes on the side of the river until we found her. She was yelling out for us to help her and stuff,'' rescuer Kya Watene said.

The 16-year-old, a year 11 pupil, was with three friends when they noticed the woman going "really fast'' down the hill.


They were giggling about the speed of it, until they saw her ''[fly] off into the river''.

The group of girls froze for a moment, but then sprang into action.

"It was just me and three of my other friends, we were just asking her what was wrong, she said she couldn't breathe, so we rang the ambulance.''

The rest of Kya's PE class, including the teacher, caught up to the group, and with instructions from the teacher, they were able to help the woman and put her into the recovery position.

"I don't know if she was ok, because as soon as the police got there we just got out of the way.''

The whole experience was "unreal'', Kya said.

The woman was taken to Waikato Hospital by ambulance for assessment.

Senior Sergeant Wayne Petherick said it was unclear if the incident was the result of a mechanical fault or operator error.

The mobility scooter was taken to Hamilton Central Police Station where it will be examined tomorrow.

Members of the public, who helped play a "major part'' in the rescue, and their actions would be recognised, said Mr Petherick.

"It's reassuring that people still have a strong sense of community, and when they see someone in trouble they step up to the mark and in this case, prevented a tragedy from occurring.''

Principal of Sacred Heart Girls' College, Chris Allen, said she was "absolutely proud'' of the girls' actions, and their "presence of mind to do what was needed''.

"It's fantastic. They did the right thing''.