The police say the incident happened about twenty past two this morning.
They say a car was seen driving erratically at about 2.20am on Thursday.
Its driver failed to stop for police and a pursuit followed, they say.
The vehicle missed a sharp left hand bend and crashed into a concrete sign near Awatapu College.
Police say the 18-year-old driver was cut from the car and is in a critical condition in Palmerston North Hospital.
Two others were treated in hospital and released.
No arrests have been made in relation to the incident.