Police and emergency services were called to the Arcadia Rd Rallysprint at the Hibiscus Coast Motorsport Club in Paparoa around 2pm, but the two had died before their arrival, a statement from MotorSport NZ said.
"The two competitors, a driver and their co-driver, were involved in a single-car incident that saw their vehicle leave the road," the statement read.
The Maungatūroto Volunteer Fire Brigade were also called to the scene.
Station officer Jodie Bennetto said when they arrived, the car had already been pulled from the water.
The crash took place on a gravel road in a rural part of the Paparoa settlement.
Firefighters helped to protect the scene.
Motorsport NZ president Wayne Christie said the whole motorsport community would understandably be shocked and upset by the terrible tragedy.
"Our thoughts are with the family and friends of these two competitors and all involved with the Arcadia Road Rallysprint. We will be offering support to all those involved in the coming days," Christie said.
MotorSport NZ said it would co-operate with all investigating agencies, as well as undertake its own full and thorough investigation.
"There are no further details to report at this time".
The fatal crash comes after two people were taken to hospital, one in a serious condition and one critical, following a motorcycle crash at the Ruapuna Raceway, west of Christchurch, yesterday afternoon.
The Herald understands the event was called "Sound of Thunder" and run by Bears Motorcycle Club.
The event said it was going to feature "iconic bikes from past and present, including the legendary Britten Motorcycle and a Moto2 replica bike".
Emergency services responded to the scene shortly before 3pm, after the motorcyclists had collided.
Earlier today, police were called to a serious crash in Kerikeri which closed State Highway 10.
Motorists were told to avoid a stretch of SH10 near Cottle Hill Drive after two vehicles crashed shortly after midday.
Police confirmed shortly after 4pm that one person had died following the crash.
"Police extend their sympathies to the family of the deceased," police said.
The road has since reopened following a scene examination and investigations into the cause of the crash are ongoing.
By Benjamin Plummer
