Locals used farm machinery to lift a tractor off the driver's arm when he was thrown off and trapped underneath in a crash on Mangakahia Rd.
The accident occurred at Awarua, about 20km south of Kaikohe, around noon on Monday.
Senior Sergeant Brian Swann, of Mid North police, said it appeared the tractor driver had failed to indicate or check for traffic before turning right into a farm driveway and was side-swiped by an overtaking Top Energy ute.
He was thrown off and pinned under the tractor by one arm.
The tractor driver was initially described as being in a critical condition so the Northland Rescue Helicopter was dispatched from Whangarei.
Kaikohe fire chief Bill Hutchinson said locals used farm machinery to lift the damaged tractor and free the trapped driver before emergency services arrived.
The helicopter landed in a nearby paddock and flew the injured man, whose condition was later downgraded to serious but not life threatening, to Whangarei Hospital for observation.
Mr Swann said the tractor driver would likely be charged with careless use of a motor vehicle. The driver of the ute was uninjured. Alcohol was not a factor in the accident.