Japan's weather agency on Saturday issued its highest alert as typhoon Halong barreled toward southwestern Japan, warning of heavy rains and strong winds from a storm that has grounded more than 470 flights.
The warning means that the storm poses a threat to life and could inflict massive damage from torrential rain and strong winds, the meteorological agency said.
The alert was issued for the Mie prefecture, some 300 kilometres (186 miles) west of Tokyo, as the outer bands of the storm was already lashing the region and other areas of southwestern Japan, the agency said.
"Please remain on the alert against a rise of rivers, floods as well as damage from landslides in Mie prefecture," the agency said on its website.
Typhoon Halong, packing winds of up to 180 kilometres per hour, could make landfall in southwest Japan late Saturday or early Sunday, according to the agency.
Television footage showed high waves triggered by the typhoon splashing over breakwaters and muddy torrents roaring down a swollen river.
Storms and torrential rain earlier this week have left one dead and four injured, public broadcaster NHK said.
At least 473 flights were cancelled due to the typhoon, which came as Japan had just begun its annual "Obon" summer holiday, NHK said.
Over the next 24 hours, the storm was expected to dump 70 centimetres (28 inches) of rain on the southwest island of Shikoku, which had already been lashed by downpours from another typhoon last weekend, the national weather agency said.
The agency also warned of major landslides and floods in other areas of southwestern Japan, while local authorities in Tokushima in Shikoku issued an evacuation advisory to some 44,100 residents, officials said.
The typhoon, which was about 150 kilometres off Shikoku's southern tip at 0700 GMT, was moving northeast at 15 kilometres per hour, the agency said.
Halong comes a month after Typhoon Neoguri killed several people and left a trail of destruction in southern Japan.
Last weekend, a man drowned in a raging river while more than half a million people were advised to evacuate as heavy rain from Typhoon Nakri lashed the country.