A Japanese official has drunk a glass of decontaminated water from the Fukushima nuclear plant to show it is safe for use.

After being grilled by reporters in Tokyo about the safety of decontaminated water from the Fukushima plant, government official Yasuhiro Sonoda produced a glass of the water and began drinking it.

The water was purified after being pumped from the basements of the number 5 and 6 reactors at Fukushima.

It had contained elevated levels of radioactive caesium.

Asked if he was trying to ease public concern, Mr Sonoda said he drank the water because he was asked to, adding that his actions do not mean the water is safe to drink.

"Just drinking [decontaminated water] doesn't mean safety has been confirmed, I know that," Mr Sonoda said.

"Presenting data to the public is the best way."

The plant's operator and the government insist the level of radioactive caesium in the decontaminated water is below the safe limit for bathing.

Radioactive contaminants spewed into the environment from the Fukushima facility following reactor meltdowns and explosions triggered by the massive earthquake and tsunami of March 11.

More than seven months after the disaster, tens of thousands of people remain evacuated from their homes and businesses in a 20-kilometre no-go zone around the plant and in pockets beyond that.

Fully decontaminating those areas is expected to take decades.

ABC/wires