Police have raided a drug rehabilitation centre this morning where a number of gang members and alleged drug dealers are on bail for serious criminal charges.

Nga Kete Wananga Solutions is a residential facility in Dairy Flat, north of Auckland, where accused criminals pay nearly $19,000 for a 12-week treatment programme including for drug and alcohol addiction, as well as family violence and parenting courses.

According to Nga Kete's website, there is "24/7 supervision" of residents who are tested twice a week for drugs and alcohol, while staff will notify police and probation services if anyone leaves without permission. Gang patches and regalia are also banned.

But the Herald can reveal that specialist police unit targeting gangs have executed a search warrant at the bail facility on Postman Rd this morning.

Officers could be seen combing a muddy paddock, probing the ground with stakes to find anything buried in the earth, and examining several shacks and sleep outs at the rear of the property.

A spokesperson for the police confirmed a "pre-planned search warrant is currently under way" at a property in Dairy Flat.

"This relates to an ongoing investigation and as such we are unable to provide further comment while our inquiries continue. Police will provide a further update when we are in a position to do so."

Officers searching a paddock at the rear of the rural property in Dairy Flat, north of Auckland. Photo / George Block

But the Herald understands that police staff from Operation Cobalt, a dedicated taskforce to investigate and disrupt gang activity, are behind the raid.

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Members of gangs such as the Head Hunters, Hells Angels and Mongrel Mob are current residents of the facility.

If the police find drugs or firearms during the search warrant, the raid will increase the official scrutiny on the services provided by dedicated bail facilities like Nga Kete.

Supporters say there is a desperate need for accommodation for bail, where residents can be supervised and receive much needed addiction treatment, instead of keeping defendants in prison while they wait for trial.

Police and probation officers, however, have raised concerns about some facilities because of the opportunities for residents with gang and drug links to live together while on bail.

In August, the Herald revealed that firearms, bundles of cash and methamphetamine had been stashed inside the Ahikaa Trust building, a bail facility in central Auckland.

"It is deeply concerning that alleged offenders are being sent to a bail and reintegration facility by the courts only to find that military-style weapons, drugs and cash are being recovered by police," the National Party police spokesman Mark Mitchell said of the Ahikaa discovery.

"It's unacceptable. If any taxpayers' money is being used to fund this facility then there are some serious questions that need answering."

Firearms, ammunition and cash found by police at the Ahikaa Trust where residents are on bail for active charges. Photo / Supplied

Minister of Corrections Kelvin Davis said it was "disappointing" the firearms were discovered at a place that provides accommodation for those who are eligible for bail, but have nowhere else to go.

"This type of accommodation is an important cog in the justice system but should be run appropriately and safely."

Davis distanced himself and his department from the Ahikaa Trust by pointing out there was no formal relationship or contract.

The incident would also be noted on any future bail application, said Davis, and Corrections staff would ask the bail accommodation facility to provide more information on its security and monitoring in bail reports.

"But again, that is for a Judge to decide."