A car has plunged into the Waipoua River in Masterton and police are seeking the owner to establish whether anyone was inside the vehicle and may have been swept downstream.
At this stage it is "too dangerous" to enter the river to check if there are any occupants.
While initial responders said it did not appear anyone was inside, police have not ruled out someone escaping and the car as it went into the river and not making it out of the water.
Police received a report of a car in the river at Opaki Road, Masterton, about 7.15am.
Since then the vehicle has been swept downstream.
"At this stage we are unsure whether there is anyone in the vehicle," said a spokeswoman.
"The vehicle was partially submerged already on arrival.
"The vehicle is now fully submerged and it looks as if we may have to wait until the river subsides before it can be removed."
Police are making enquiries to locate the owner of the vehicle.
A Westpac Helicopter has been dispatched to the scene.
"The helicopter ran a search of the area but nothing of interest located and the river is too dangerous for further investigation at this time," said a second police spokeswoman just before 11.30am.
"On arrival emergency services located the car partially submerged and it appeared there was no one in the vehicle.
"A Life Flight helicopter conducted a search and did not locate anything to suggest a person was in the water.
The vehicle has now been submerged and swept downstream.
"The conditions are too dangerous to pull the vehicle from the river or deploy Police's Dive Squad.
"Police are concerned that someone may have gotten out of the vehicle and gotten into trouble in the water."
Anyone who witnessed the crash, or may have any other relevant information, is asked to contact police on non-emergency line 105 and quote event number P043828970.