A fourth person has been hospitalised after taking an unknown drug in Wairarapa.
Police said officers were called to a Masterton home about 8.50pm on Wednesday, where a person was in a critical condition after consuming a "white powder substance".
The person was taken to hospital where they received naloxone, a drug that reverses an opioid overdose.
It comes after three people were found unresponsive at a property in the small Wairarapa village of Tinui on Saturday.
All three people had taken an illicit substance, which they believed to be cocaine.
It prompted a High Alert to be published by Drug Information and Alerts Aotearoa New Zealand (DIANZ) for the white powder. It said the presumed cocaine has suspected to be misrepresented or adulterated with an unknown opioid.
While all four people have recovered, police said they are "extremely concerned" at the significant risk of harm or death.
"We are investigating to determine what the substance is, where it came from, and how far it is circulating, but urge anyone with white powder to be extremely cautious," Wairarapa Relieving Area Commander Inspector Nick Thom said.
"If you or someone you know takes a white powder and starts to experience unusual effects, call 111 immediately."
The police would like to hear from anyone who might have information about this substance or its origins, or anyone involved in its distribution.
"If you can help, please use our 105 service. You can also share information anonymously through Crime Stoppers on 0800 555 111."
