"What this tells us is the fentanyl was cut or diluted by this sugar-type substance," MacDonald said.
The drug is highly potent and easy to overdose on and is believed to be behind a significant increase in drug overdose deaths in the United States.
MacDonald said in North America last year, more than 60,000 people lost their lives due to a fentanyl overdose.
"The discovery of powdered fentanyl in New Zealand is of significant concern, due to the harm caused internationally by the synthetic opioid," MacDonald said.
"Just one gram of pure powdered fentanyl is the equivalent of 20,000 safe doses of the drug."
"We do not want to see that type of harm occurring in our communities," MacDonald said.
"Police are now working urgently to determine the source of the drug and its prevalence in the community."
Further sample tests related to the Wairarapa hospitalisations are ongoing.