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The family of a teenager killed in a high-speed crash want to know if a police car was pursuing the vehicle before the accident after claims by two passengers and an independent witness.

Police say they were not chasing a Subaru WRX carrying four teenagers when it left the road at Dairy Flat, north of Auckland, on Easter Monday.

Front seat passenger Jamie Lance McElrea, 17, died the next day after he was thrown through the rear window and hit a lamp-post.

It is not known if Mr McElrea was wearing a seatbelt, although his family said they would be surprised if he was not because he was apparently telling the driver to slow down as the speed topped 200km/h.

A police spokesman said the fatal crash was not being treated as a pursuit but the Police Complaints Authority had been notified.

"My understanding is that at the time of the crash there was no police pursuit in progress and in fact there had not been an actual pursuit taking place," said spokesman Kevin Loughlin.

He refused to go into detail, but said the Subaru had "attracted the attention" of a police officer in an unmarked car.

Mr Loughlin would not say what action was taken by the police officer but "he eventually came upon the scene and alerted the Serious Crash Unit".

Backseat passengers Kayla Hewison and Matthew Anderson, who were also thrown from the car, claim a police car was pursuing them before the crash - and Ms Hewison alleges the vehicles came into contact.

In a signed statement Ms Hewison, 18, said a police car was "right up our butts". She said "the cop pulled out of a street and started following us".

Driver Troy Andersen remarked "oh ****, this isn't gonna happen today".

Mr Andersen started "boosting" and was travelling at 160km/h, with speeds reaching 220km/h, Ms Hewitson said.

"Everyone was yelling and saying 'boost it, boost it'."

"Then the cops caught up to us, we had stopped at the intersection [of Pine Valley Rd and Kahikatea Flat Rd] then the cops were right up our butts. We went left, boosted it, cops were up our butts again. We felt a bang, we all went forward a bit then I remember sliding and then I remember starting to flip."

Ms Hewitson's statement recalled Mr McElrea had said "slow down Troy, **** man stop, we're all gonna die".

Ms Hewitson, who was thrown through the back window but escaped with rib injuries and scratches, said she had also given a statement to police in which she alleged the police car was following close to the Subaru "and gave us a bump".

She said the car had lights and sirens going at the time.

Ms Hewitson said police told her "that's your side of the story".

Police are yet to interview Mr Andersen. His mother said he would not comment on the accident.

Asked if police were pursuing her son at the time of the crash, she said: "Bits and pieces have come up but we're really not in a position to discuss it at the moment."

Matthew Anderson said via text message that police were pursuing the vehicle.

"Yes they were but im guna talk 2 a lawyer b4 i say nethin else."

He said he could not remember how close the police car was travelling to the Subaru, or if the vehicles came into contact.

Jamie's father Mark McElrea had also spoken to an independent witness who was passed by the speeding Subaru and a police car just before the crash.

Mr McElrea said a Dairy Flat resident travelling on Kahikatea Flat Rd told him the Subaru overtook him and his partner on a dangerous corner. He was overtaken about 50m further along the road by a police car with lights flashing.

"Less than a kilometre later he comes across the crash," Mr McElrea said.

"The cop car is parked way down past the accident. The driver [of the police car] made a u-turn and headed back towards the accident, where he parked in a driveway."

Another local man said he also saw the Subaru and police car.

The man, who did not want to be named, said the police car had lights flashing but in his opinion there was no pursuit. The police car was at least 500m behind the Subaru when they passed his house.

Mr McElrea said police started "closing shop" when asked about allegations of a pursuit. He was amazed they had yet to interview Mr Andersen.

"We're entitled to some answers and we're not getting anything," he said.

Jamie McElrea was working in the boat building industry and had just been accepted into the Army when he died.

His kidneys and corneas have been used in transplants, while his pancreas and heart valves will be used when needed.

His aunt, Kellie Tremayne, said her nephew made a decision to be in the speeding car and the family were not trying to paint him as a saint, but "whoever contributed to this chain of events has to be made to stand up".

Lawyer John Moroney, who is acting for the McElrea family, said it was a distressing time.

"All they're looking to do is get to the truth of the matter and from what's been ascertained so far there are a number of questions that need to be answered, and there's been some reluctance on the part of those involved to discuss what happened that day."

A spokesman for the Police Complaints Authority said it was notified of the accident because "there was an element of pursuit".