The Parliamentary Commissioner for the Environment is warning against buying waterfront properties, saying they will be gone within decades.
Jan Wright's report on the effects of sea-level rise on New Zealand has found sea levels have risen 20 centimetres in the last 100 years, with another 30 centimetres expected by 2050.
Dr Wright said some councils have started dealing with the imminent problem, but more councils needed to respond.
"But it's very difficult because not only is it people's homes and properties, it's a lot of public infrastructure - roads and rails and sewage systems and storm-water systems... All of these things could be under threat."
Dr Wright looked at about 200 years of scientific study of sea levels for the peer-reviewed report.
The report released yesterday is the first of a pair examining sea-level rise in New Zealand.
It also warned New Zealanders should expect more severe floods in future - like those seen in January 2011 in Auckland, which caused damage worth $7 million.
According to NIWA, a storm of that measure will now hit every 10 years by about 2040 - and, a few decades later, every year.
According to the report, Christchurch has already gone through changes, with earthquakes resulting in some land slipping by about a metre, increasing the region's vulnerability to king tides, storm surges and floods.
The second report, due to be released next year, is expected to show in some detail which areas of the country's coastline will be most vulnerable to rising seas and floods.