Police say the bomb squad had to be called in when grenades and explosives were found during a raid on a methamphetamine lab.
Police executed simultaneous search warrants in Ngaruawahia and Blockhouse Bay last Friday with support from the armed offenders squad.
Thousands of dollars' worth of equipment, including surveillance cameras, was discovered during a weekend examination of six shipping containers and three caravans.
Detective Sergeant Nina Pedersen, of the Avondale CIB, says the investigation started two weeks ago and officers weren't expecting to come across such a sophisticated commercial-scale laboratory.
Two Auckland men, 37-year-old David Griffiths and a 43-year-old, have been charged with manufacturing methamphetamine and will reappear in court at the end of October.