The move comes as a widespread radiation scare in South Korea is leading to a sharp drop in the consumption of fisheries products, reports YonhapNewsAgency.
"The measure comes as our people's concerns are growing over the fact that hundreds of tons of radiation contaminated water are leaked daily from the site of Japan's nuclear accident in Fukushima," the Ministry of Oceans and Fisheries said in a press release.
"The measure also comes as the government concluded that it is unclear how the incident in Japan will progress in the future and that the information the Japanese government has provided so far is not enough to predict future developments."
The government had imposed an import ban on some Japanese fisheries products soon after an earthquake in March 2011 led to the meltdown of a nuclear reactor at the Fukushima plant.
The import ban was later expanded to include 50 products from Fukushima and seven other nearby prefectures. They are Ibaraki, Gunma, Miyagi, Iwate, Tochigi, Chiba and Aomori prefectures.
"Under the new measure, all fisheries products from this region will be banned regardless of whether they are contaminated or not," the ministry said.
When even a minuscule dose of radioactive material, such as cesium or iodine, is detected in any products from any other region of Japan, the government will request additional radiation tests by Japan and their results before allowing shipments of such products into South Korea, it said.
"This will effectively keep out any fisheries products that are contaminated even a little by radiation," the ministry said.
In addition, the government has decided to lower the allowed dose of radiation in fisheries products from the current 370 becquerel per kilogram (Bq/kg) to 100 Bq/kg.
An official from the National Fishery Products Quality Management Service earlier said a person is exposed to the same amount of radiation when taking a single x-ray picture as a person who eats a fish with a cesium level of 370 Bq everyday for eight months.
"Along with its measures, the government has again urged the Japanese government to immediately provide accurate information on the leak of radiation contaminated water at Fukushima nuclear power plant," the ministry said.