UN chief Ban Ki-moon arrived in Japan on Sunday, where he plans to visit the Fukushima nuclear disaster zone, as the crippled atomic power plant simmers and a food safety scare deepens.

The secretary general will visit hard-hit Fukushima prefecture as one of the most senior foreign leaders to go to the area after a magnitude-9.0 earthquake and tsunami on 11 March triggered the catastrophe.

On Monday, Ban will meet some of the 85,000 people who have been evacuated to shelters from areas around the plant after what has become the worst nuclear disaster since Chernobyl 25 years ago.

"I wanted to come to Japan as soon as possible after the tragedy of 11 March to express the solidarity and deep sympathy that the whole world feels for the people of your great country," Ban said last week.

The UN chief will also meet Prime Minister Naoto Kan and Foreign Minister Takeaki Matsumoto later on the same day in Tokyo.

Ban has convened a nuclear safety summit for the UN General Assembly in New York in September and is expected to reinforce his calls for tougher international standards while in Japan.

Ban plans to visit Haragama beach at Soma, 40 kilometres (25 miles) north of the Fukushima Daiichi plant, which continues to leak radioactive material. A 20-kilometre exclusion zone around the battered facility prevents him going much nearer.

Five months on from the disaster, the Japanese government and operator Tokyo Electric Power Co (TEPCO) are struggling to stabilise three reactors that have melted down.

Lethal hotspots were detected inside the crippled nuclear plant last week with radiation so high that it would kill a person within weeks if they were exposed to it for even one hour.

While the government plans to bring the overheating reactors to stable "cold shutdown" by January, Kan has declared his determination to reduce Japan's dependence on nuclear power.

Takashi Sawada, vice-chairman of the Atomic Energy Society of Japan, said the Fukushima plant still posed risks despite some progress reported by the government.

"We still need to watch out for strong aftershocks and tsunamis, which could throw back the effort to control the accident," Sawada said. "Workers will need to continue decontaminating radioactive water to prevent it from overflowing.

"Recently found hotspots also risk hindering workers from making progress."

TEPCO has faced a series of technical glitches with a system to decontaminate radioactive runoff water used to cool the troubled reactors.

Radioactive substances from the plant continue to contaminate the food chain, with bans on produce widening from some green vegetables to milk and dairy products, river fish, mushrooms and green tea.

The Japanese government has also imposed a ban on beef from the northeastern region, citing elevated radiation levels in the meat of cows.

Japanese consumers are especially concerned about rice, the country's staple food, as the harvest season approaches, with local authorities hurrying to inspect radiation levels.

In his meetings with Japanese leaders, the UN chief is also expected to request Japan's Self-Defence Forces be dispatched for a peacekeeping operation in South Sudan.