Storm surge flooding is starting to occur more frequently on the highest tides, the National Institute of Water and Atmospheric Research said.
Sixty-five percent of New Zealanders live within 3 miles of the sea and the country must plan to manage the growing risks, said Rob Bell, the institute's principal scientist.
Twelve of the country's 15 largest cities are within that 3-mile band.
"Rises of more than a meter by 2100 can't be ruled out, and should at least be considered in assessing the vulnerability of our existing development at the coast," Bell said in a statement.
With rising sea-levels, low-lying coastal areas would face an escalating risk from sea flooding if the sea level rose by 1.6 feet, he said.
Scientists will present their projections for sea-level rise and its impact on the coastal environment at a New Zealand Climate Change Center conference in Wellington May 10-11, China's Xinhua News Agency reported.