The supply and demand of Japan's stockpiled nuclear materials is imbalanced, triggering safety concerns that could affect the world, a Chinese study revealed Friday.

"The fact that Japan accumulates more and more weapon-grade fissile materials, especially separated plutonium, will put Japan, and its neighboring countries and the whole world at risk," a joint study by China Arms Control and Disarmament Association and the China Institute of Nuclear Information and Economics said.

With the Rokkasho reprocessing plant starting operation next year, the problem could become worse and may lead to a vicious cycle.

Citing the latest data from the Japanese government submitted to the International Atomic Energy Agency (IAEA), the study found Japan has 47.8 tonnes of highly sensitive separated plutonium, 10.8 tonnes of which are stored in Japan, enough to make 1,350 nuclear warheads.

"Once the Rokkasho reprocessing plant under construction starts its operation, Japan could obtain the ability of producing eight tonnes of separated plutonium annually," the study said.

In addition, Japan has about 1.2 tonnes of highly-enriched uranium (HEU) for research reactors, according to the study.

"Japan does not need that much enriched uranium for producing nuclear energy. So we are suspicious for any ulterior motives by the Japanese government to invest such a large amount of money in that," Zhu Xuhui, a senior consultant affiliated with the China Arms Control and Disarmament Association said.

"Japan's nuclear materials problem is not insolvable," Chinese Foreign Ministry spokeswoman Hua Chunying said in response to the issue.

"The linchpin lies in its sincere and responsible attitude, adopting tangible measures to address the concerns of the international community," she said.

The study suggests Japan should make a rational plan for its nuclear materials consumption, address the imbalance, while ensuring the safety and security of these materials.