Experts from the International Atomic Energy Agency met Japanese officials Monday as part of a mission to assess clean-up efforts at the crippled Fukushima nuclear power plant.

The UN atomic agency began the nine-day mission at the request of the Japanese government, as it did in 2011 following a powerful earthquake and tsunami that sparked reactor meltdowns at Fukushima.

The plant's operator has struggled to contain radioactive contamination, admitting in July that highly toxic water from the site may have leaked out to sea.

"The international community and the agency in particular are very interested in following the recovery activities in Japan," Juan Carlos Lentijo, director of the IAEA's nuclear fuel cycle and waste technology division, told Japanese officials at the environment ministry.

Lentijo will lead a 16-member team of experts to tour polluted areas near the stricken Fukushima plant, some 220 kilometres (140 miles) northeast of Tokyo

Lentijo told reporters the team hoped to advise on the clean-up as well as ways of dealing with radioactive waste.

Vice Environment Minister Shinji Inoue told IAEA officials: "We have great expectations that you will provide us with significant advice from international and professional standpoints."

A massive earthquake and tsunami in March 2011 devastated Japan's northeast coast and sparked reactor meltdowns at the Fukushima plant by knocking out its cooling systems.

The plant has continued to leak, with some radioactive water suspected of flowing into the Pacific Ocean.

Tens of thousands of people who were evacuated from the Fukushima region are still unable to return to their homes, with scientists warning some areas near the plant will have to be abandoned forever because of radioactive contamination.