A fourth person - an elderly man - has been rescued and was being taken to hospital via rescue helicopter.
Emergency services were called to a report of a vehicle underwater in a farm pond in the central North Island on Sunday morning.
Police were alerted to the incident in Raetihi, in the Ruapehū district, just after 11am.
"Tragically the three people were deceased when recovered from the pond by emergency services," police said in a statement.
"Police are working to support the family of those killed. WorkSafe has been notified."
The Palmerston North Rescue Helicopter attended and a spokeswoman confirmed a fourth person was being air lifted from the scene about 2.40pm.
She said he was an "elderly man" and he was en route to Whanganui Hospital in a moderate condition.
The property where the car is understood to be submerged is less than a kilometre out of Raetihi's township.
Raetihi is about 87km inland from Whanganui and close to Tongariro National Park.
The property is 74.5ha and the owners operate a farm improvement business from it, offering diggers, trucks, bulldozers and fencing materials.
Tassia Allum, an employee at Caltex Raetihi, said about 11am she had heard sirens, with two ambulances, a fire truck and a police car all headed up State Highway 4.
Her colleague Craig Hughes had seen a rescue helicopter landing across the road in the cemetery before flying toward Auckland.
Ruapehū District Council chief executive Clive Manley said he could not comment as police were in the early stages of their investigation.
