Japan started releasing treated radioactive water from the wrecked Fukushima nuclear power plant into the Pacific Ocean on Thursday, a polarising move that prompted China to announce an immediate blanket ban on all aquatic products from Japan.

China is “highly concerned about the risk of radioactive contamination brought by… Japan’s food and agricultural products,” the customs bureau said in a statement.

The Japanese government signed off on the plan two years ago and it was given a green light by the U.N. nuclear watchdog last month. The discharge is a key step in decommissioning the Fukushima Daiichi plant after it was destroyed by a tsunami in 2011.