Police were called to an address in Korito, 16km south of New Plymouth, just before 7pm on Saturday.
A spokeswoman said a man had died in a rural area and a homicide investigation had been launched.
"Police were called to a property in Korito [following] reports a man had been seriously injured," she said.
"On arrival, the man could not be revived and he died from his injuries."
"The Armed Offenders Squad responded, and around 9pm took a man known to the victim into custody.
Police said they were not looking for anyone else in relation to the death.
The homicide investigation is ongoing.
• Anyone with information that could assist with the investigation can call police on 105, and quote file number 200823/6014. Information can also be provided anonymously via Crimestoppers on 0800 555 111.