Since breaking out on Wednesday in a mountainous area of Otsuchi Town, the fire has destroyed eight buildings, including residential houses, Kyodo News reported.
Otsuchi has issued evacuation orders to nearly 2,600 people, about one quarter of the town's population.
Helicopters from the Iwate prefectural government and the Self-Defense Forces were mobilized for water-dropping operations, and personnel from fire departments across the prefecture were deployed.
Firefighting assistance from Hokkaido, Yamagata, Fukushima, Tochigi, and Niigata prefectures has also been requested.
Furthermore, following a 7.7-magnitude earthquake that struck off northeastern Japan on Monday, the Japan Meteorological Agency has issued a special weeklong quake alert for 182 municipalities across seven prefectures, including Iwate. Authorities have warned that vigilance is required for earthquake risks while responding to the fire.