A powerful typhoon looming down on disaster-ravaged Japan has killed at least four people, authorities said Wednesday, less than a month after a vicious storm left 100 dead.

Rescue workers transport evacuees in a boat through floodwaters in Nagoya in central Japan\'s Aichi prefecture on September 20.

More than a million people have been warned to leave their homes over fears that the torrential rains Typhoon Roke is expected to bring will cause widespread flooding.

Four people have been found dead in central and western Japan, while two people are missing in Gifu prefecture, including a young boy who disappeared on his way home from primary school.

Evacuation advisories have been issued to a total of 1.14 million people nationwide, according to broadcaster NHK. It was not clear how many had followed the advice, which falls short of mandatory evacuation orders.

Auto giant Toyota said it was temporarily shutting 11 of its 15 Japanese plants, which lie in the path of the approaching storm.

"The second (afternoon) shift is stopped. (It is) not resuming today. No decision has been made for tomorrow," company spokesman Dion Corbert told AFP.

The affected plants are all in Aichi prefecture in central Japan.

Roke is expected to heap more misery on a country that has suffered badly under the yoke of nature this year.

The huge earthquake and tsunami of March 11 left 20,000 people dead or missing and devastated hundreds of kilometres (miles) of coastline, destroying whole communities and wreaking billions of dollars of damage.

The Fukushima Daiichi nuclear power plant was sent into meltdown after its cooling systems were swamped by the waves, sending radiation into the air, sea and food chain in the planet\'s worst atomic disaster since Chernobyl.

Earlier this month Typhoon Talas slammed into central Japan, killing around 100 people in the deadliest storm to hit the country for over 30 years.

Heavy downpours caused flash flooding and massive landslides that swept away buildings and people.

By Wednesday morning, Typhoon Roke was off the Kii Peninsula in central Wakayama prefecture.

It was expected to make landfall in the Kanto area in the afternoon before moving northeast, possibly towards the crippled Fukushima nuclear plant where workers are still battling to control persistent radiation leaks.

"The typhoon will move north at high speed," a Japan Meteorological Agency official told a news conference, warning of damage and impact on transportation systems.

The typhoon has already brought torrential rain and some flooding, with TV footage showing residents walking through streets knee-deep in water.

A number of expressways have been closed, while more than 200 flights are to be cancelled for Wednesday, according to NHK.

In the city of Nagoya, a regional commercial hub located near the home of Toyota Motor, about 380,000 households remained under evacuation advisories, media reports said.

Nagoya mayor Takashi Kawamura warned: "Please follow evacuation advisories as soon as possible in order to prevent people from falling victims."