China's blanket radiation testing on seafood imports from Japan introduced earlier this month is estimated to cause some ¥100 million ($720,000) in damages to five Japanese companies, with the losses expected to widen, sources familiar with the bilateral relationship said Thursday.

The five firms had fresh fish and other imported items kept in southern China for prolonged procedures that require about two weeks for chilled seafood and about one month for frozen ones to clear customs, the sources said.

The newly implemented testing is seen as a move to pressure Tokyo over its plan to release treated radioactive water from the damaged Fukushima nuclear plant into the sea starting this summer.