The Department of Conservation says the number of kiwi in an unfenced zone on the Coromandel Peninsula has doubled in the past 10 years.
The Moehau kiwi zone was set up in 2000 and is protected by a network of 1700 traps.
DoC says the area now has nearly 300 brown kiwi, compared to about 130 a decade ago.
Ranger Michael Walker says brown kiwi at Moehau are increasing by 14% per year, meaning the population will double every five years.
But, without protection, he says there won't be any kiwi on the Coromandel Peninsula in 100 years.
Mr Walker says eight out of every 10 chicks in the zone survive to adulthood, compared to unprotected areas where 19 out of every 20 die.
Dogs are the major threat.