Police say they still do not know how many people were in the car that plunged off a bridge near Harihari on the West Coast almost 24 hours ago.
They said the red 2014 Toyota Corolla was heading south from Greymouth on State Highway 6 when it went onto a one-lane bridge and crashed through the barrier into the Wanganui River.
The crash happened at about 4.30pm yesterday afternoon.
Rising river levels are hampering efforts to retrieve the car, which is believed to be in an underwater hole about five metres deep.
At a press conference this afternoon, Inspector John Canning said they believed conditions should improve enough to get the car out tomorrow.
Mr Canning said so far no one had been reported missing and police were still seeking information from local accommodation providers and the public about who the occupants might be.
He said he believed the bodies were likely to be trapped in the vehicle as helicopter searches have found no sign of anything downstream.
Dispute over river hazards
Rafting specialist Josh James Marcotte said he was ready and willing to search the river for the occupants soon after the crash yesterday but was stopped by police.
Witnesses said the car plunged off the bridge at speed and reported seeing up to four people in the vehicle before it crashed.
The police dive squad and a crane have been called in to help with the search but heavy rain has swollen the river, hampering efforts to retrieve the car.
A police spokesperson said earlier that nothing could be done until the river subsided.
Mr Marcotte said a friend who was first on the scene called him and they were quickly ready to search the river; he was frustrated police stopped them.
"It was perfectly safe, we had a look at the hazards, there was very minimal hazard, so we were perfectly safe to jump in there," he said.
"We are both certified swift water rescue technicians and the police said 'no, you're not getting in there'.
"They obviously had no idea of the hazards. They just wouldn't let us get in there and do our job, which was very frustrating."
Police should recognise certified water experts who are not with Search and Rescue, Mr Marcotte said.
Mr Marcotte and his colleague saw a piece of wreckage bobbing up and down.
"We just saw a piece of red come up and down. Two of the other witnesses, one thought they saw a set of tail lights and another guy thought he saw a door, so it sounded like the vehicle was bobbing around just under the surface."
Police have asked local accommodation providers to come forward if any of their customers failed to show up last night.