Japan is coming under increasing pressure to expand an evacuation zone around the battered Fukushima nuclear plant.

The UN watchdog the IAEA and Japan’s own nuclear safety agency have both recommended widening the zone from 20 to 40 kilometres.

Radiation in the sea nearby has now hit 4,000 times legal limits.

But government officials are warning against overreaction, saying radiation levels away from the plant are still low-risk.

“We’ll continue to monitor the radiation in the air and make all preparations necessary so that when the need arises, we’ll be able to deal with it without delay,” said Chief Cabinet Secretary Yukio Edano.

But he acknowledged that high radiation levels found in the soil could pose a danger to health in the long term.

French President Nicolas Sarkozy is in Tokyo, the first foreign leader to visit since the earthquake.

He has suggested a meeting of nuclear officials from G20 countries in Paris in May, to determine new global safety standards.

France is the world’s most nuclear-dependent country. Earlier, the head of French nuclear energy firm Areva arrived in Japan with a team of experts, to help Fukushima’s operators Tepco bring the plant under control.