SOUTH Korea has banned all fishery imports from a swathe of Japan around the crippled Fukushima nuclear plant, dealing another blow to Tokyo's credibility on the eve of its bid to host the Olympics.

Just hours after Prime Minister Shinzo Abe broke away early from the G20 summit to personally back Tokyo's bid to host the 2020 Summer Games, Seoul extended a ban on 50 imports from eight Japanese prefectures, including Fukushima, due to concerns about radiation contamination.

A spokesman for the South Korean Prime Minister's office said: "The measures are due to the sharply increased concern in the public about the flow of hundreds of tonnes of contaminated water into the ocean at the site of the Fukushima nuclear accident in Japan."

Korea's indefinite ban, which takes effect on Monday, affects some of Japan's biggest fishing areas and increases pressure on the country to fix the crisis.