"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!"