A powerful typhoon is heading for Japan's Fukushima prefecture and other areas hit by the 11 March earthquake and tsunami, after leaving at least four people dead in the country's central region.

The meteorological agency warned that the typhoon, the second to strike Japan this month, was generating winds of up to 130mph (209 km/h).

Tokyo Electric Power (Tepco) said strong winds and torrential rain had so far not caused damage to the Fukushima Daiichi nuclear plant, although the area had yet to feel the full force.

"The biggest cause for concern is the rise of [radioactive] water levels in the [reactors'] turbine buildings," said Junichi Matsumoto, a Tepco spokesman.

The firm said cooling systems used to keep the reactors stable would not be endangered by the typhoon, adding that every possible measure had been taken to prevent leaks of radioactive water.

"We expect to be able to withstand [an overflow] even if water levels rise suddenly," Matsumoto said.

According to Tepco estimates, the plant's reactor buildings contained more than 1m litres of radioactive water as of the middle of September.

Earlier, more than a million people in central areas had been urged to evacuate.

Evacuation advisories had been issued to 1.3 million people, including 800,000 in the city of Nagoya, 170 miles west of Tokyo. Most advisories had been lifted by early afternoon, but remained in place for 330,000 people in the most vulnerable regions.

Typhoon Roke does not appear to have caused as much damage as some had initially feared, but strong winds and driving rain led to the cancellation of train services in Tokyo, stranding tens of thousands of commuters. Power was cut to more than half a million homes in Tepco's service area, including the capital.

The firm said more than 575,000 households were without electricity, while several other companies, including Toyota and Nissan, were forced to close plants as a precaution.

Media reports said four people had died in central and western Japan, including a middle-aged man whose body was discovered in a river in Nagoya on Wednesday morning. Police in Gifu prefecture said a nine-year-old boy and an 84-year-old woman were missing after reportedly falling into a swollen river.

The typhoon caused strong winds, heavy rain and high waves in central Japan before heading towards Tokyo and north-eastern regions.

The government advised people to remain vigilant until the storm had passed.

"We need to exercise maximum caution against heavy rains, strong winds and high waves in wide areas from eastern to northern Japan," the chief cabinet secretary, Osamu Fujimura, told reporters.

The meteorological agency warned that rivers in parts of central Japan were overflowing. NHK television showed residents in some areas wading through knee-high water. The typhoon dumped as much as 400mm (16ins) of rain in some areas on Wednesday.

"In Aichi the heavy rain is causing some rivers to overflow," an agency official told reporters. "I would like to ask people to exercise caution against potential disasters from torrential rain, strong winds and high waves."

Roke's arrival comes two weeks after typhoon Talas triggered floods and mudslides that left 67 people dead and 26 missing. In 2004, typhoon Tokage killed 95 people.

The meteorological agency described Roke as "very strong" and advised residents living in its path to exercise the "greatest possible vigilance".

The approaching typhoon also caused disruption to factories and power output.

Chubu Electric Power, which supplies the central region, said it had lost 1,870 megawatts of hydropower output but there was no threat of electricity shortages.

About 450 domestic flights were cancelled and some bullet train services were suspended, including the busy route between Tokyo and Osaka.

Toyota, meanwhile, said it would close 11 factories in central Japan early to ensure the safety of employees. The carmaker said it would make up for lost output on subsequent shifts. Many commuters in Tokyo have been advised to leave work early.

Heavy rain was expected to continue in many areas of Japan's main island of Honshu until Thursday morning, according to Kyodo news agency.