A nuclear engineering expert, who's visited the Fukushima power station, told RTHK on Thursday that an independent investigation should be carried out at the tsunami-devastated nuclear facility before treated radioactive waste water is released into the Pacific Ocean.

Dr Luk Bing-lam, from City University of Hong Kong, backed calls for such a probe after an International Atomic Energy Agency (IAEA) review of Japan's plan declared it within international safety standards.

However, he said the UN nuclear watchdog had not given Tokyo the green light to release more than a million tonnes of contaminated water into the sea.

"The IAEA neither recommended or supported this action," Luk said. "They reviewed the safety of this process [discharging the contaminated water] and they believe it follows the IAEA safety standards."

He told RTHK's Hong Kong Today that the issue is that the IAEA report is based on a lot of information provided by Tokyo Electric Power Company (TEPCO) which manages the Fukushima-Daiichi Nuclear Power Plant.

"For me, personally, I would like to see a more independent organisation to provide that information."

Luk said he'd studied the IAEA report on the planned Fukushima discharge and it was mostly a review of the information provided.

"Although they did do the comparison tests on the treated water, most of the report is reviewing what TEPCO and the nuclear regulatory agency [of Japan] .. information provided by them."

He said this had not given him sufficient evidence to support that this is totally safe.