People may not be able to live in areas near Japan's radiation-spewing nuclear power plant for up to 20 years, an adviser to Prime Minister Naoto Kan's government said yesterday.

Kenichi Matsumoto, a consultant to the prime minister's Cabinet Secretariat, initially told Japanese media that the remarks had been made by Kan when they met at his official residence earlier in the day.

But the 65-year-old academic, who has written many books on wide-ranging subjects including modern history and philosophy, said later the remarks were his own.

"You may not be able to live there for the time being," Matsumoto first quoted Kan as telling him about the areas from where residents have been evacuated, according to the Jiji and Kyodo news agencies and the TBS network.

"It would be something like 10 years and 20 years."

The government has set a 20-kilometre exclusion zone outside the plant.

It said on Monday it was to widen the evacuation area due to radiation leaks from the Fukushima Daiichi plant, which was crippled by a massive quake and tsunami on March 11.

Matsumoto later told media that he received a call from the prime minister about the comment.

"It was my own. The prime minister may share the perception but he did not say such a thing at all," Matsumoto said.

Prime Minister Kan also told reporters later he did not make such a comment.

Matsumoto said he had proposed to Kan the idea of building an ecologically-friendly town inland with space for 50,000 to 100,000 people to help resettle evacuees who may have to abandon their homes near the plant.