SEOUL (Reuters) - South Korea President Yoon Suk Yeol had a seafood lunch on Monday, his office said, to allay public concern over the safety of local fish products after Japan began discharging treated radioactive water from its Fukushima nuclear plant.

Japan started releasing water from the wrecked plant into the Pacific Ocean on Thursday, sparking protests in Japan and neighbouring countries. Chinese consumers have been particularly upset, and Beijing has announced a blanket ban on all aquatic products from Japan.

In South Korea, the government has said it has found no scientific or technical problems with the release, but public concern remains high over seafood and ocean contamination.

During his weekly meeting with Prime Minister Han Duck-soo, Yoon had a seafood lunch. The presidential office cafeteria also had raw fish on the lunch menu for its staff, it said.

Tests of seawater near the Fukushima plant have not detected any radioactivity, Japan's environment ministry said on Sunday, days after the discharge began.

Fishery industries, however, still fear a sharp decline in seafood consumption. In a July public survey by pollster Media Research, 62% of South Koreans said they would cut back or stop consuming seafood once the discharge goes ahead, despite government assurances that it would closely monitor the release.

Kim Hi-soo, 55, a vendor at Noryangjin, the largest fish market in Seoul, said on Monday: "One of our regulars came days ago and said he came to consume as much as he can before (the discharged water) spreads ... It's heartbreaking ... when I think about the slump that we'd have to face in months."

(Reporting by Soo-hyang Choi and Daewoung Kim; Editing by Tom Hogue)