Six people have been arrested, two of them senior patched members of the Mongrel Mob. Bomb disposal procedures were being followed in relation to the grenade.
They said earlier that approximately $400,000 cash had been recovered, as had 10 firearms and two motorbikes estimated to be worth up to $30,000.
The arrests follow what is said to be a significant police investigation targeting the supply and distribution of the Class A drug in the Wellington region by members of the Mongrel Mob in Porirua.
A police statement said several residential properties were searched by officers this morning.
"A number of safes were also found during the searches, the contents of which are yet to be examined by police.''
The Police Asset Recovery Unit had been helping the investigation team.
Together, they had restrained more than $1.8 million worth of assets.
Those assets include two residential properties, 13 vehicles, two boats and a jet-ski.
Detective Inspector Mike Arnerich said: "Today's arrests follow a lengthy investigation by Wellington Police into the supply and distribution of a significant amount of methamphetamine...in the Wellington region by members of the Porirua Mongrel Mob.
The amount of meth the gang members are believed to have been working with is about 20kg.
The six people arrested include a 48-year-old man and a 34-year-old woman from Auckland.
The pair were arrested this morning and will appear in the Manukau District Court this afternoon.
In total, the group face 52 charges. Further charges may follow, police say.
Arnerich acknowledged that the monetary value of the meth they had recovered was significant - but not as much as the social cost of the drug getting into the community.
"We've shown today that police will use everything in our power to dismantle and destroy drug dealing syndicates and prevent the social cost methamphetamine inflicts on our families and communities.''