The typhoon categorised as 'strong' by the Japan Meteorological Agency (JMA) was expected to bring torrential rain, strong winds and a storm surge, EFE news reported.
Namtheun, the twelfth typhoon of the season in the Pacific, was located between Kyushu and Okinawa at 12.00 p.m., moving at 15 kmph in a northwestern direction.
Between Saturday and Sunday, Namtheun was expected to pass over the southwestern coast of Kyushu, the third-largest island in the Japanese archipelago, and cause rainfall of some 80 mmph, generating winds of up to 190kph.
Authorities have warned against the risk of floods, landslides and a storm surge, advising residents to remain indoors.
Earlier this week Japan was hit by another typhoon Lionrock that claimed the lives of 16 persons and the numbers were expected to rise as rescue operation continued in northern Japan.
Rains caused by Lionrock led to overflowing rivers and severe flooding.
