Lynam said three of the five people in the Corolla had died and the other two were in Waikato Hospital in a serious but stable condition after undergoing surgery last night.
"Initial indications are that one vehicle ended up in a ditch and the other later caught fire following the crash."
Lynam said it was a "terrible and tragic time for the families" of the people who had died.
Police were working to establish the identities of the victims so they could notify the next of kin and were unable to confirm the sexes of the people who died. No more details would be released at this stage.
The serious crash unit is investigating the cause of the crash and police wanted to speak to any road users who saw either of the vehicles just before the accident at about 7.30pm.
Lynam said police would not know the cause until the investigation had been completed, but confirmed there was heavy fog in the area at the time of the crash.
"It's too early to determine what the factors are. The investigation is still ongoing."
The crash occurred north of Netherton School, not considered a high-risk crash area.
Rescuers worked throughout the night at the crash scene. The road has since reopened but the crash site is littered with debris from the wrecked vehicles and the smell of burnt rubber.
An eyewitness told the Herald he helped pull two French nationals from one of the vehicles, which had flipped, trapping them inside. The survivors could not speak English.
Another witness told Fairfax four or five French tourists appeared to have been travelling together in one of the cars and had only been in the country for a day.
"I couldn't understand much of what they were saying and the only other information we could get from them was that they were from France," the Netherton resident said.
One or two people were thought to have been travelling in the second car, which exploded in flames, with the force of the explosion rocking nearby homes.
While two of the French tourists were pulled to safety, the resident believed at least two other people from the tourists' white car had perished.
Another resident who lived nearby told Fairfax he heard a loud crash, followed by an explosion, then looked out his window to see a vehicle engulfed in flames.
"I chucked my high-vis vest on and ran out to help.
"The car that was on fire ... there was no helping the people in there. It was too late to get the fire extinguishers, the flames covered the whole of the car.
"It wasn't until the fire was put out that you could see there was [at least one] body," he told Fairfax.
"I got a torch and started searching the drain for bodies because it was dark and I wasn't sure if there were people flung from the car."
The man found the tourists' vehicle crashed off the road and helped firefighters get one of the survivors out by stretcher.
Other witnesses to the aftermath of the crash told the Herald of hearing screams for help.
One man who rushed to help two people trapped in one of the vehicles said rescuers encountered a "giant orange fireball" and heard "screams" coming from one of the cars.
Marcia Audain and her partner Roger Farley were heading back to Waiuku when they came across the foggy crash site where a car was on fire.
Audain said a truck driver yelled to them "I need help, I need help". The next moment the burning car "just exploded".
"It was the worst thing I have experienced," she said.
"The force of the explosion sent the truck driver flying down the bank. That was the moment that happened we realised what we had just come across."
Farley and Audain then realised there was another car down the bank. Farley ran down the bank to the other vehicle and saw there were two people moving.
He forced the doors open and called out for a knife to cut the seatbelts.
"My first thought was get the door open and get them out. I called out for a knife to get the two guys I could see alive out," Farley said.
"They were in a bad way but one said 'no English' and I asked where he was from and he said France."
Farley said the time until emergency services arrived was a blur.
"There was four or five of us helping to get them out, some up to their knees in mud."
Farley said he didn't know first aid so just worked at keeping the men alert.
Aucklander Hamish Anderson, who was travelling to Auckland with his wife, was behind one of the cars involved in the crash.
He said heavy fog meant visibility was reduced to about 20 metres.
"I'm pretty shaken up," he said. "The thought that me and my wife were three or four cars back and another 500m it could have been us. And then seeing people like that ..."
Anderson arrived on the scene seconds after the crash.
"There were screams - not from the car that was in flames - they must have already been dead - but from the car that was in the ditch," he said.
"A few of us tried to get close but the other car was still exploding - literally explosions coming from the vehicle."
Anderson parked his car about 100m back and told his wife to stay in the car and went to try and help.
Fire Service northern shift manager Jaron Phillips said one of the vehicles in the crash was "well involved" in fire when emergency services arrived.
