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.
"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!"