A 15-year-old girl, the sole survivor of a fatal car crash after a police pursuit in Palmerston North, remains in a serious but stable condition.
A 12-year-old girl who was in the front seat died at the scene after the car hit a power pole after a 90-second chase.
The 15-year-old boy driving the stolen Subaru died later in hospital.
Police said he was driving in breach of bail conditions and failed to stop when signalled to by an officer.
The Serious Crash Unit and the Independent Police Conduct Authority are both investigating the crash.
The crash brings the number of fatal pursuits this month to four, with five deaths in total.
A youth advocate wants to know how the teenage boy got back behind the wheel of a stolen car.
Billy Meehan said he wanted to know why the boy was not being closely monitored, given his history of dangerous driving.
He said the deaths were devastating.
The deaths bring the number of people killed while fleeing the police in the past two years to 21.
Just over a week ago a 15-year-old, who was travelling in the boot of a car that was being pursued, died when the vehicle crashed.
A man died in Kawerau on 11 May when he crashed after fleeing from police.
And on 7 May another driver died minutes after a pursuit was called off, after the fleeing car crashed into a power pole.