China's biggest salt maker urges public not to panic buy after Fukushima discharge

China's biggest salt producer urged people against panic buying after Japan began discharging treated radioactive water into the Pacific Ocean from the wrecked Fukushima nuclear plant on Thursday, despite firm opposition from Beijing.

The state-run National Salt Industry Group, the world's biggest common salt producer, said in a statement issued hours later that it was ramping up supplies as people in some parts of China had rushed to stock up.

Salt shelves were emptied in supermarkets and sold out in online sales platforms in some places, including Beijing and Shanghai.

China has opposed Japan's action, saying the Japanese government had not proved that the water discharged would be safe and has banned the import of all aquatic products from Japan.

"We are working overtime to produce, distribute and making all efforts to guarantee market supply," the National Salt Industry Group said in its statement.

"Please purchase rationally and do not panic buy blindly," it said.

The national salt group said sea salt only accounts for 10 per cent of the salt people consume, the rest are well and late salt, which are safe from contamination.

The group said its salt supply is ample and the stock shortfall would be temporary.

Japan has criticised China for spreading "scientifically unfounded claims" and maintains the water release is safe, noting that the International Atomic Energy Agency (IAEA) has also concluded that the impact it would have on people and the environment was "negligible".