The Auditor-General's office says less than half of all public assets are insured, but that is not necessarily cause for concern.
Following the Christchurch earthquakes, the office surveyed 400 public entities about their insurance policies for assets worth $225 billion.
The Auditor-General's report says some Government departments, councils and other public agencies analyse their risks and self-insure while others simply do nothing as they consider insurance too expensive.
Nationwide, 40% of premiums had increased by more than 20% between 2011 and last year, and many organisations reduced their cover or increased excesses to keep costs down.
The report shows that the Transport Agency, Auckland Council and its subsidiary Watercare account for the largest proportion of uninsured assets.
The report says the police self-insure, and district health boards arrange collective insurance to make savings on brokerage fees and premiums.
It says some public entities need to ensure risk assessments are done, to make better decisions about insurance.