In Godzilla (1998), the monster lizard is from the area around the nuclear test sites at Mururoa Atoll and Fangataufa Atoll, which are located in French Polynesia.
In the original film, it is somewhere off the coast of Odo Island. In the Showa era, it is on Monster Island; in Heisei, Birth Island; and in the Millenium series, it seems to be somewhere around Guam.
Japan