The foreign ministry on Friday expressed "extreme regret" over Japan's two-week quarantine plan for visitors from South Korea over new coronavirus concerns, warning of "all possible" corresponding measures.

Vice Foreign Minister Cho Sei-young plans to summon Japanese Ambassador to South Korea Koji Tomita to officially lodge a protest over the measure that is set to take effect Monday and last until the end of this month.

Tokyo announced Thursday that visitors from South Korea and China will have to stay at designated facilities for two weeks to be checked for infections and refrain from using public transportation. It also plans to suspend the 90-day visa-free entry program for South Koreans on Monday.

"We express extreme regrets over the fact that Japan has taken such an unreasonable and excessive measure without sufficient consultations with us, although our government has urged Japan to cautiously review its additional measures multiple times," the ministry said in a text message sent to reporters.

"We strongly urge Japan to immediately reconsider this measure," it added.

The ministry also raised doubts over Japan's intentions behind the latest step.

"Given that this measure came when signs of progress in our containment efforts appear to have emerged, we cannot help but doubt whether Japan has other intentions than its considerations of the quarantine aspect," the ministry said.

"While placing the top priority on the health and safety of our citizens, the government is weighing all possible measures (in response to Japan's measure)," it added.

Japan has already banned the entry of people who have visited the southeastern city of Daegu and the adjacent Cheongdo County, where the bulk of the country's COVID-19 infections have taken place.

Japan's latest restrictions angered South Korea in particular because Seoul has refrained from such extraordinary steps against Japanese nationals even at the onset of the outbreak on a virus-hit cruise ship off its coast.

Critics raised speculation that Tokyo might have decided to tighten restrictions on the entry of Koreans to help circumvent domestic criticism of Prime Minister Shinzo Abe's handling of the virus outbreaks.

The presidential office Cheong Wa Dae is set to convene a National Security Council meeting to discuss measures in response to Japan's latest step.

As for the possible measures, observers said that Seoul could consider restricting the entry of people from Japan and halting the 90-day visa-free program for Japanese visitors.

But South Korea could face a dilemma, as it has not taken any tit-for-tat steps against the countries that have been enforcing entry bans or other forms of restrictions on Korean travelers.

In particular, Seoul did not take any action after Chinese provincial authorities quarantined some 860 South Koreans as precautions.

As of Thursday afternoon, South Korea has reported 6,088 confirmed cases of the novel virus and 42 deaths. As of 1 a.m.

Friday, 100 countries and territories planned to enforce or were imposing entry restrictions or stricter quarantine programs for people from South Korea. (Yonhap)