A boat collecting seawater for monitoring radioactive materials in the sea is seen near the Fukushima Daiichi Nuclear Power Plant. (Photo: Reuters)

Japan on Thursday started releasing water from the wrecked Fukushima plant into the Pacific Ocean, sparking protests within Japan and neighbouring countries and prompting China to ban aquatic product imports from Japan.

The ministry’s tests of samples taken from 11 points near the plant concluded concentrations of radioactive isotope tritium below the lower limit of detection - 7 to 8 becquerels of tritium per liter. It said the seawater "would have no adverse impact on human health and the environment".

The ministry will publish test results weekly at least for the next three months, an official said.

Japan's fisheries agency said tests of fish from near the plant did not show any abnormalities. Its test on Saturday found no detectable levels of tritium.