TOKYO -- More South Koreans are visiting Japan this year as they shun China amid worsening relations between Seoul and Beijing.

South Korean visitors to Japan in May surged 85% on the year to 558,900, according to data released Wednesday by the Japan National Tourism Organization. Japan received a total of 2.29 million visitors during the month, up 21.2%.

"South Korean tourists' country preference changed to Japan from China due to the THAAD issue," said Won Young-jin, a manager at Mode Tour, a major travel agency in South Korea. He was referring to the Terminal High Altitude Area Defense system that the U.S. brought to South Korea due to North Korea's numerous missile launches this year.

Beijing, which fears the system could also peer into Chinese air space, retaliated against South Korea by banning tour groups to the country. Now it appears South Korean tourists are striking back themselves by boycotting China.

Mode Tour said the number of South Koreans visiting Japan in the period of March through May surged 72% from year-earlier levels. The agency also said the number visiting Southeast Asia jumped 66% during the same time frame.

"Tour demand for Japan will continue to rise if there is no political issue or natural disaster as Japan is becoming more affordable for Korean tourists," the manager said. "Japan is a secure tourism destination with many delicious foods."

The number of South Korean visitors to China during the same period plunged 42% on the year, according to Mode Tour data.

Looking at Japan's foreign arrivals by country for the first five months of the year, only South Korea showed year-on-year growth of more than 20% each month. So far this year, Japan has received more visitors from South Korea -- 2.83 million, up 38.9% -- than from any other country. China, which used to top the list, is now No. 2 at 2.69 million, up 8%.

To meet the rising demand for flights to Japan, South Korea's Jeju Air, T'way Air and Air Busan -- all budget airlines -- are adding flights. This summer, South Korean carriers will make 882 flights per week to Japan, around 20% more than last year, according to Japan's transport ministry.

Meanwhile, total foreign visitors to Japan this year topped the 10 million mark on May 13, 23 days earlier than last year and the earliest date ever for the country to welcome that many tourists. In April, 2.58 million foreign tourists arrived in Japan, the highest total ever for any single month.

Nikkei staff writer Kim Jaewon in Seoul contributed to this story.