Civil Defence says it didn't have the right information to issue a timely tsunami warning following November's 7.1 magnitude earthquake off the East Cape.
Residents evacuated to higher ground after the earthquake hit in September. Photo: Supplied / Ali Rewi
An internal review has found 31 issues with Civil Defence's response, including the 80-minute delay before a tsunami warning was issued.
That warning came 45 minutes after small tsunami waves hit.
The ministry's director, Sarah Stuart-Black, said officials had to wait for experts to review the earthquake and provide advice on the likelihood of a tsunami.
She said if Civil Defence consistently pre-empts that advice, it runs the risk of crying wolf and the public tuning out.
"If it's an earthquake above a certain size then we can immediately issue warnings. The problem is when it falls below that threshold and it may or may not have created a tsunami."
She said the ministry is looking at how it can get the alerts out faster.