The latest was a 31-year-old woman who died Thursday evening in Auckland. Police suspect she was smoking synthetic marijuana shortly before her death though other factors may have contributed.
Synthetic marijuana is made with chemicals similar to those found in natural marijuana to give users a high. It is illegal in New Zealand, where authorities say the drug is dangerous and is sometimes laced with other chemicals.
Chief Coroner Judge Deborah Marshall said the drug can cause seizures and many people have been hospitalized after using it.
"While the police and coronial investigations are still at an early stage, and the final causes of death have yet to be established, the number of cases where synthetic cannabis appears to have been a contributing factor has prompted me to issue this public warning," Marshall said in a statement last week, before the latest two deaths.
Police say they're aware of speculation a specific "bad batch" may have caused the deaths but they don't have any scientific proof of that.
Acting Detective Inspector Peter Florence said Friday police were taking the problem seriously and doing everything they could to get the drug off the streets.
"Every day, police officers across the country are conducting search warrants and seizing synthetic cannabis and we are continuing to put suppliers and manufacturers before the courts," he said in a statement.