"It was awful. It really was. It was a hell of a crash. I was saying, don't move anybody, but of course they were dragging them out. How do you know if it's a back [injured] or whatever?"
The woman told Fairfax a girl in the car said she had told the driver "he was going too fast, but he wouldn't listen".
Frantic relatives of the injured children arrived at the accident site as emergency services were dealing with the crash.
The woman said the driver was trapped and another boy had a badly injured arm.
Meanwhile, Nikau's cousin said Fairfax the youngster would "never be forgotten".
"He will always remain in our hearts and I give all the support to the family who grieve for him. We once had a brave soldier whose time has come to an end but we will cherish every second we have spent with him rest easy little brother. Love and miss you forever and always."
A tangi was expected to be held at Turangawaewae Marae sometime next week.
Nikau's family are in tatters and another three families face an anxious wait as they keep bedside vigils for the six other children who were hospitalised with serious to critical injuries.
Police said the children came from four Ngaruawahia families and many were related, either as siblings or cousins.
It was not clear yet who was driving the vehicle but nobody in the white Toyota Wish was old enough to obtain a driver's licence.
The registered owner of the car was known to the children, police said.
A member of the Ngaruawahia community said the shattered family of the 11-year-old had to make the call to turn off the boy's life support.
Another member of the community said she did not want to comment because "four families are obviously pretty devastated."
A community board member said there had been a meeting of friends connected to the families on Saturday morning and a decision was made not to speak to media until the families were ready.
Waikato District mayor Allan Sanson said the crash would hit the tight-knit community hard.
"It's really tragic this has actually happened. You've just got to feel for the families involved."
Sanson said the crash was "catastrophic" for the tiny Waikato town because most people would know the children or their whanau.
It's understood some of the children attend Waipa Primary School in the town.
"This will really hurt the community."
Sanson was disturbed that the children had access to a vehicle but "in saying that we all leave our keys lying around".
"I don't know the circumstances around that."
Tributes have begun to surface on social media. One person said the dead boy still had a lot to offer the world and thanked whanau for their support.
Maurice Dalziel, a resident on the street where the crash happened said he felt his house shake when the car hit the tree metres from his home.
"I was actually sitting here watching TV1 just after 6pm and suddenly there was a sort of a bang and I thought it was an earthquake."
Dalziel said he thought his roof was falling in.
"I went around the front and then I spotted it, a car had gone up into a tree."
His neighbours rushed to the aid of the children before emergency services arrived.
Waikato Police are investigating the crash and said it was too early to determine who was driving or the cause.
"This is an absolute tragedy for a number of families and the community as a whole," Detective Senior Sergeant Stephen Ambler said.
"All of the youths are local to the area and our thoughts are with the family and friends of all those involved."
Ambler said police were calling for witnesses who may have seen the white Toyota Wish between 5pm and 6.15pm in the Ngaruawahia township on Friday.
"Inquiries are continuing with the registered owner of the vehicle, who is known to the occupants of the vehicle.
"While our thoughts are with the families of those involved, police are urging drivers to exercise caution on the roads, to drive to the conditions and to ensure people behind the wheel know their limits," Ambler said.
Anyone with any information about the crash can contact Detective Sergeant Andre Kavanagh of Hamilton CIB on 07 858 6200.
Alternatively, details can be passed anonymously to Crimestoppers on 0800 555 111.
