By Agence France-Presse
Typhoon Trami, packing maximum gusts of 216 kilometres (134 miles) per hour near its centre, was forecast to hit the mainland early Sunday and could cause extreme weather across the country into Monday.
Television footage showed branches ripped from trees by strong winds blocking a main street in Naha, with massive waves splashing on breakwaters on a remote island in the region and torrential horizontal rain.
Some 600 people evacuated to shelters in Okinawa and electricity was cut to more than 121,000 homes, public broadcaster NHK said.
At least 386 flights were cancelled mainly in western Japan, according to public broadcaster NHK.
Five people suffered injuries in storm-related accidents in Okinawa, but no one was feared dead, local officials said.
"The number may rise as we are still collecting information," said Motoki Minei, an official at the island's disaster-management office.
"We are urging our residents to stay vigilant against the typhoon," he told AFP.
The weather agency warned people across Japan to be on alert for "violent winds, high waves, heavy rain."
After raking the outlying islands, the typhoon is forecast to pick up speed and approach western Japan on Sunday, remaining very strong as it barrels over the mainland.
Fishermen in Kagoshima bay, where the typhoon is expected to make landfall, were already making preparations, tying down their boats as Trami approached.
Angler Masakazu Hirase told AFP: "It's dreadful because we already know there's another typhoon after this one but you cannot compete with nature. We do what we can to limit the damage."
If the forecast holds, it will be the latest in a series of extreme natural events to strike Japan.
Western parts of Japan are still recovering from the most powerful typhoon to strike the country in a quarter of a century, which claimed 11 lives and shut down the main regional airport in early September.
Deadly record rains also hit western Japan earlier this year and the country sweltered through one of the hottest summers on record.
Also in September, a magnitude 6.6 earthquake rocked the northern island of Hokkaido, sparking landslides and leaving more than 40 people dead.