Jumping into rough surf in jean shorts and a singlet to rescue a man and his 7-year-old daughter left a born-and-bred Tauranga woman wondering why others did not do the same.

Erin Spencer, who lived in Welcome Bay until she moved to Auckland five years ago, was at Goat Island, near Leigh, north of Auckland, when she heard the cries for help.

"I heard the girl. I initially thought I had it wrong then I heard the daughter," Ms Spencer said.

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Ms Spencer, who was at the beach with her 5-year-old daughter, Mia, had packed up and was just about to leave the beach at 4pm, when she saw two people in trouble in the water.

"I could see the father was struggling to get in, the girl was really starting to panic," she said. "He was continuously trying to battle the rolling waves and hold his daughter up."

The pair, who were about 25 to 30 metres out, were fighting against the waves at Goat Island, which according to Ms Spencer was "the roughest I've ever seen it".

Ms Spencer had just completed her PADI Rescue Diver Course in December, and had the knowledge still "fresh" in her mind.

Standing with about seven other people who were watching the situation unfold, she looked about for a flotation device such as a boogie board. Unable to find anything close she knew, "it was basically now or never". She swam out with the "quite serious waves" crashing on her.

When she finally got to the pair, she approached cautiously and allowed for space as she approached them. In some cases people in similar situations may launch themselves at rescuers, pulling them under the water.

Luckily, "He just wanted me to take over holding the daughter. He was going under as he couldn't hold his daughter and he wasn't able to help himself. He would have ended up drowning. The father was that exhausted, he dumped his daughter in my arms."

Ms Spencer said the young girl was "hysterical the whole way back, crying out for her dad".

The father was able to bring himself to shore. Once there, both he and his daughter were bleeding from injuries sustained from rocks. Aside from the injuries from the rocks, both were "utterly exhausted and emotional", but unharmed. The father, who Ms Spencer thought was Greek from his accent, "kept saying 'thank you, thank you so much".

Ms Spencer advised that if in the same rescue situation, "you need to put yourself first".

"I don't think I would have done what I did if it wasn't for that training," she said. "It probably made the difference between me and everyone standing there. "

Ms Spencer said if possible taking a flotation device out was important, as was knowing if you are "capable of the rescue", and even having basic knowledge of first aid. Ms Spencer's father, Pyes Pa resident Clive Spencer, said he was "very proud of our girl".