The tsunami-triggered meltdown at a Japanese nuclear power plant last year offered important lessons in protecting such facilities from terrorism, Japanese Prime Minister Yoshihiko Noda said Tuesday.

Noda told a nuclear security summit in South Korea that people in charge of securing atomic energy facilities around the world must not be lulled into a "myth of safety", whether in regards to a natural disaster or terrorist attack.

Noda said the disaster at the plant at Fukushima had shown the difficulties in preparing for the worst-case scenario, when officials could not comprehend the scale of the threat to the nuclear power plant.

In the case of Fukushima, officials had only prepared for a tsunami just over five metres (16 feet), but the the waves that swamped the coastal plant were three times higher, according to Noda.

"The workings of nature are beyond comprehension, but there is also no limit to human imagination," Noda told the leaders or top officials from 53 nations attending the summit, including US President Barack Obama.

"We should keep in mind that the man-caused act of sabotage will test our imaginations far more than any natural disaster."

Noda said the most important lesson to be learnt from the Fukushima meltdown was that there was no end in the efforts to ensure safety.

"Every person who works towards nuclear security should take this to heart," he said.

The tsunami, in March last year, knocked out cooling systems at the Fukushima plant, sending three reactors into meltdowns that led to radiation leaking out over a wide area.

Tens of thousands of people were forced from their homes and vast swathes of farmland were contaminated in the world's worst nuclear accident for a quarter of a century.