Health workers say an increase in the number of mistakes made at hospitals stems from a lack of funding and staffing.
The Health Quality and Safety Commission's annual report released on Thursday found there had been 437 medical mistakes in the country's district health boards, a 21% rise on the previous year.
The chair of Patients' Rights Advocacy in Waikato says there are many repeated mistakes, often with little explanation from hospitals. Carolyn McKenzie says district health boards are struggling to meet growing demands.
Association of Salaried Medical Specialists executive director Ian Powell says the understaffing he's seen of senior doctor roles does not promote and maintain safety.
The commission said on Thursday the increased number of events stems not so much from more accidents happening than from more people reporting them when they do.
Many of the incidents involved people being injured from falls while in hospital. Others included a heart procedure performed on the wrong person, incorrect prescription of drugs and delays in providing treatment.