Tourism officials are concerned about a drop in October of visitors from South Korea, the largest source of tourists for years.

The officials blame the Fukushima nuclear disaster, saying South Korean tourists have generally always shrugged off political tensions, such as the Takeshima/Dokdo territorial dispute.

A decrease in Japan's biggest source of visitors "for the past 20 years could shake the tourism industry," an official with the Japan Tourism Agency said following Wednesday's release of the October estimate of 929,000 foreign visitors, a monthly record and up 31.5 percent from a year earlier.

Taiwanese topped the list with 213,500 tourists, up 58 percent from a year earlier, followed by South Koreans at 158,300, down 5.9 percent, and Chinese at 121,400, up 74.1 percent.

According to the Japan National Tourist Organization, the United States sent the most visitors from 1964 through 1988.

South Korea jumped to the top spot following its liberalization of international travel for the 1988 Seoul Olympics and maintained the top position through last year, with the exception of 1998.

For many South Koreans, Japan is seen as a familiar and nearby destination. It is common for tourists to depart South Korea on Friday night and late Sunday night on flights that take only around two hours.

Kyushu and its hot springs are popular with Korean tourists, but they also visit other destinations across Japan. Okinawa and Akita prefectures became popular after they were used as locations in South Korean TV shows.

While tourists from China fell significantly due to the Senkaku Islands row, Korean tourists, especially young ones, used to be largely unaffected by political tensions, the agency said.