Power has been cut across 30 towns and cities, with the blackout causing a temporary closure of Kansai International Airport near Osaka.
Typhoon Trami, rated category 2 by Tropical Storm Risk, with category 5 the highest, is the latest storm to threaten Japan in a year of weather-related woes, including punishing heat, heavy rains and landslides.
Up to 20 inches of rain are forecast to hit Japan, with the storm currently packing winds of 100mph.
Outlying islands in the Okinawan chain, 620 miles (1,000km) southwest of Tokyo, were being pounded by heavy rain and high tides a day before an Okinawan gubernatorial election on Sunday.
Strong wind knocked down trees, blew off an outer wall from a building and left nine people injured in Okinawa.
About 22 people are thought to have been injured with flying glass and debris blamed for the majority of injuries.
About 600 people have been evacuated in Okinawa city.