The Ministry of Health has expressed concerns after four patients died in the past year at Auckland District Health Board's acute mental health inpatient service.
A briefing paper to new Health Minister David Cunliffe said a review was under way.
The paper was written at a time when appropriately qualified individuals had been invited to submit proposals for carrying out the review.
"The ministry has existing concerns about clinical safety and quality issues in ADHB's acute mental health inpatient service, following the deaths of four patients over the past 12 months," the ministry said.
The November 2 paper said the review was scheduled to begin within the next fortnight.
A spokeswoman said Mr Cunliffe was not going to comment while the review was under way.