Bystanders rushed to help a young girl caught up in a water incident at a holiday park in the Firth of Thames.
Emergency services were called to the Miranda Holiday Park just after 8pm, police said, after reports of an incident involving a child.
Members of the Auckland Westpac Rescue Helicopter arrived to find people carrying out CPR on the child after a dramatic rescue.
A spokesman said bystanders managed to pull the girl out of the water and start CPR before paramedics arrived.
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"CPR was being conducted on her, on our arrival.
"Her condition was initially critical, but improved to serious condition on transport to Starship (Children's Hospital)."
A St John incident report said they were called to a "water incident". However, police said it was possible a medical event had occurred.
Miranda Holiday Park issued a message on their Facebook page alerting people to the situation.
"Sadly, last night, we had a water incident involving a young child.
"Please take this as a reminder wherever you are this summer - to keep a watchful eye on your children in and around any water."
Staff later updated their message to say: "The child is recovering well!"