Typhoon Neoguri bore down on the Japanese mainland Wednesday after slamming into the southern Okinawa island chain, killing two people in the country and leaving a trail of damage.
Packing gusts of up to 180 kilometres (110 miles) per hour, the typhoon could 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 torrential 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.
By Wednesday afternoon the typhoon was some 400 kilometres (250 miles) away from the west coast of Kyushu and was churning north in the East China Sea at 25 kilometres per hour.
The weather agency warned that as much as 300 millimetres (12 inches) of rain could fall on Kyushu in just 24 hours through noon Thursday.
Kyushu, situated next to the biggest island of Honshu where major cities including Tokyo and Osaka are located, was already experiencing heavy rain and strong winds.
Authorities were likely to issue an emergency alert for residents to seek shelter before Neoguri's landfall.
On Monday officials issued their highest typhoon alert for Okinawa, warning that Neoguri -- which means raccoon in Korean -- could turn deadly.
On Wednesday, the weather agency's chief forecaster Satoshi Ebihara said the situation in Okinawa remained serious even as the typhoon moved out to sea, with the agency issuing a fresh rainfall alert.
Okinawa was still dealing with a "situation that we've never seen before" due to heavy rain, he said, adding that a "serious crisis" was possible.
"It would be no surprise if this unprecedented torrential rainfall triggers a serious disaster with landslides and flooding," he said.
Just over 52,000 households had no power as of noon Wednesday in Okinawa, while schools were closed with air and sea traffic halted.
In just 12 hours, Okinawa's main island was hammered by twice the amount of rainfall that usually falls in the entire month of July.
Some in the village of Yomitan were shocked to see muddy water splashing into their homes as heavy wind and rain pummelled the area.
"I'm 89 years old and this is the first time I've experienced something like this -- nature can be overwhelming," an elderly woman in the village told public broadcaster NHK.
In the Okinawan capital of Naha, trees were split, signboards flew about and a restaurant was destroyed.
Dozens were injured across the archipelago.
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 southwestern Kumamoto prefecture.
Other areas of Japan also saw heavy rain.
The island of Sado, in the Sea of Japan (East Sea) which faces the centre of the country, saw 110 millimetres (4.3 inches) of rain in just three hours Wednesday morning. The weather agency described it as "torrential rain seen once in 50 years", NHK reported.