The French military has confirmed that platforms have been built on Moruroa atoll, should a coral cliff collapse trigger a huge wave and force the 35 military personnel deployed there to seek safety.
Addressing the media in Tahiti after touring the area, Commodore Anne Cullerre says, however, radiation from the former nuclear weapons test site poses no risks.
The atoll in French Polynesia was used until 1996 for more than 130 underground blasts and remains a closely monitored military exclusion zone.
The French High Commissioner Jean-Pierre Laflaquiere has dispelled concerns about a possible atoll collapse that could trigger a 20-metre high wave.
He says such an event would not be sudden and allow for Moruroa to be evacuated and the residents of nearby Tureia to be warned.