Civil Defence is seeking photos or video footage of a tsunami wave hitting Christchurch's estuary.
It says a video clip of a wave taken during February's tsunami alert is one of the most valuable tools scientists have in assessing the potential impact of a larger tsunami.
Waves generated by an 8.8 magnitude earthquake in Chile hit New Zealand without causing serious damage, but authorities say that would have been a different story in parts of Canterbury had it been high tide.
Civil Defence is working to develop a tsunami resilience plan for the vulnerable coastal community of Southshore.
On Monday night residents were told of a different risk factor as the spit they live on could be hit by water from two directions.
The authorities say footage such as that of the estuary is invaluable and if people have more it will help with developing a safety plan.