Police have confirmed one person died at the scene of the incident on Chapel St, which was first reported just after 5pm. A St John spokeswoman said three others were injured and treated at the scene.
The incident happened at the traffic lights at the turnoff into the shops.
A Fire and Emergency NZ spokesman said a three-vehicle crash had been reported, with one vehicle "submerged" in the water.
Witness Errol Hodgson told the Bay of Plenty Times he was driving home from work when he saw two vehicles crash at the Chapel St lights then a third, an SUV, come "out of nowhere".
"The SUV went up over the island and straight over the edge [into the water].
"It went down real fast.
"I stopped here [about 20m away] and ran over there. The rear window was disappearing.
"The windows must have been down because it went down so fast, it was ridiculous."
He said a man got out of the sinking car.
"They tried to get the other person out. They were there a long time. The car kept moving down there because of the currents. It's still there.
"There were people running everywhere."
Kran Radford and Rem Mangakahia were also driving home when they saw the commotion.
Mangakahia said: "We saw everybody started to run so we parked up, we wondered if we should help. Everyone was running and diving in..."
"They were trying to get dive bottles and stuff from the [hunting] and fishing shop to help.
"They did pull out a lady. They put her on some sort of floating board and carried her [out]."
Radford said there were about 20 people in the water, including children, so they did not get in.
Another witness estimated the person was trapped in the car for 15 to 20 minutes.
A worker in the area said she heard a "big bang" and people started running outside.
By the time she got outside, she saw a vehicle was in the water near the traffic lights.
"Police were trying to rescue someone ... I could see people swimming, trying to get someone out [of the vehicle]."
"I could hear someone crying."
Another witness said a person from Rebel Sport, located across the road, supplied goggles to help people see through the murky water.
Police said an investigation was ongoing.
