KEY POINTS:
A major drug bust yesterday broke up a multi-million-dollar P ring being run from inside prisons, police say.
More than $5 million worth of the drug was seized.
Twelve people were arrested in the sting - eight of them prisoners at Auckland Prison at Paremoremo and the Spring
Hill Correction Centre in Waikato.
Police expect to make more arrests.
Twenty-three homes around Auckland were raided yesterday and the two prisons were "locked down" while searches were carried out. Police say the six-month operation involved 120 officers with 60 Customs and prison staff.
Neither the Corrections Department nor police are saying how prisoners have been involved in a drug ring from behind bars.
"That will obviously form part of our evidence so that will come out as things progress through court," operation commander Detective Inspector Steve Wood told the Herald.
"They're there [in prison] on other matters and this investigation will be laying further charges against eight of them."
Two of the accused are women. All 12 will appear in the North Shore District Court on Monday on charges including manufacturing and supplying Class A drugs and the importation of precursor chemicals.
Mr Wood said over a six-month period, Customs NZ had intercepted 20kg of Contac NT, a Class A chemical used in the manufacture of P, which had come from China.
A Customs NZ spokesman said that was enough to make 5kg of P. At a price of about $1000 per gram, the haul has a street value of $5 million.
Most of the chemicals were intercepted at the International Mail Centre near Auckland Airport but more had been sent in courier parcels.
Police discovered a hydroponic cannabis-growing operation, firearms, cash and methamphetamine in yesterday's raids.
Mr Wood said these items were not found within either prison.
He wouldn't say how police became aware of the drug ring, for operational reasons.
The value of the items seized had not yet been added up, with still more to come.
"It's likely there will be further arrests over the next few days or weeks because there are a large number of inquiries to follow up."
Police said the sting, dubbed Operation WEB, launched in January to "investigate importation and distribution of controlled and precursor drugs in NZ by a well-organised group of criminals".
"This operation has involved specialist and highly trained professionals from within all three agencies combining as a team, to jointly neutralise an extremely sophisticated and well organised group of criminals," Mr Wood said.
Warren Cummins, Northern Regional Manager for Corrections, said prison staff assisted in the raids.
"The operation went smoothly and there were no serious incidents.
"A number of prisoners from both these prison sites assisted police with their enquiries."