Typhoon Nanmadol made landfall near the city of Kagoshima, on Japan's southern island of Kyushu, bringing winds of at least 180 km/h, local media reported.
The cyclone is expected to provoke rainfall during the day, with flooding and landslides expected to follow, according to the Japan Times.
Officials issued a "special alert" for the life-threatening storm and advised over four million people to evacuate, the media outlet said.
