Recent tsunamis in other parts of the world, such as the 2011 Tohuku tsunami in Japan and the 2009 South Pacific tsunami, were larger than scientists had considered likely to happen in those regions, leading to greater uncertainty about what New Zealand could face.
Because of this, the GNS Science report increased the estimated hazard in areas most exposed to locally triggered tsunamis, which includes Tauranga.
In the 2005 GNS Science report, the estimated height of a tsunami hitting Tauranga was 4.7m, which has been increased to between 8m and 10m in the new report. In August, the Bay of Plenty Times reported on a Tauranga City Council workshop which said in a worst-case scenario, Tauranga could be hit by a 14m tsunami triggered in the Kermadec Trench.
GNS senior scientist Graham Leonard said the difference between this report and the August workshop was how the wave height was measured. In yesterday's report, the measurement was based on how high the wave would be before making landfall, whereas Dr Leonard said it was likely the council's report was based on the size of the wave on land.
The August report was also based on a worst-case scenario, while yesterday's report used average wave heights, he said.
Bay of Plenty Civil Defence and Emergency Management Group chairman John Forbes said there was potential for a larger wave to be generated than previously thought, but flooding and volcanic eruptions were the more likely causes of an emergency.
A significant tsunami would impact across the Bay, but that was unlikely to happen in the lifetimes of people alive today.
"If a tsunami is generated close to shore, we aren't going to have enough time to warn people. If there is an earthquake strong enough people are struggling to stand up, if you are in a low-lying area, as soon as the shaking stops, make your way to higher ground."
The report said about 10 tsunami of 5m or more had hit New Zealand since 1840. The historical record of dangerous tsunami triggered locally suggested nearby events happened every 40 to 50 years on average.
Mr Forbes said there was "quite a lot of history" of tsunami in the Bay, but most did not do any harm.
"Most tsunami, like most earthquakes, don't hurt us that much. It's like when Ruapehu has a bit of a puff, it may disrupt the flights for a day or two but that's about it."
Mr Forbes said there was planning on a regional basis around being disaster-ready, including local energy companies and sewerage and water networks, but none of this would matter if individuals and families were not prepared.
