Typhoon Neoguri headed for the Japanese mainland on Wednesday after crossing to the southern Okinawa island chain, killing two people and leaving a trail of damage.
With gusts of up to 110 miles an hour (180km/h) the typhoon was forecast to hit the southern main island of Kyushu as early as Thursday before moving east along the Japanese archipelago, the national weather agency said.
Officials said Neoguri would bring heavy rainfall and warned of the risk of flooding and landslides after the storm – which has weakened from a super typhoon – forced half a million people to seek shelter in Okinawa on Tuesday.
Kyushu – next to the biggest island of Honshu, where major cities including Tokyo and Osaka are located – experienced heavy rain and strong winds. Authorities were considering an emergency alert for residents to seek shelter ahead of Neoguri's landfall.
On Monday authorities gave issued their highest typhoon alert and on Wednesday the weather agency said the situation in Okinawa remained serious because of the prospect of further torrential rain bringing the possibility of landslides and flooding.
In the Okinawan capital of Naha on Tuesday traffic lights went out, trees were split, signboards flew about and a restaurant was destroyed.
The coast guard and local police said a 62-year-old man was found dead after he was knocked off his boat in rough waters near Japan's mainland, while public broadcaster NHK said an 81-year-old fisherman died in south-western Kumamoto prefecture.
Schools were closed, air and sea traffic ground to a halt and nearly 70,000 Okinawan households had no power.