"We worked on him for an hour and we started his heart again but he's still very, very sick."
Last night, a distraught member of the boy's family said they were "very shaken" about what had happened.
Victim Support personnel were speaking with the family but they were too upset to talk to the media.
In a statement, Police said the young boy was seen to be unresponsive on the bottom of the pool about 11.10am.
He was rescued and given CPR.
"He was revived but is in a critical condition and has been flown to Starship Hospital by the Westpac Rescue Helicopter," the statement said.
"The child was visiting the pool with his family. Police are providing support to the family."
Police are investigating the circumstances of the near drowning and said no further information could be provided at this time.
The manager of Palm Springs Thermal Pool, which is about five minutes from Helensville, said he could "neither confirm nor deny where it [near drowning incident] happened".
"I'm not at liberty to say anything about anything that happened here today."
The man, who would not give his name, later said "everything's under investigation" and to phone back later this afternoon.
"Ring me back and then I can give you some details then."
A tradesman was working at the pools when the incident occurred.
"I heard they got a heartbeat, that's all," he told the Herald.
He would not comment further.
A WorkSafe NZ spokeswoman said they had been notified and were making initial inquiries into the incident.
