South Korean pharmacists issued an appeal Thursday cautioning against panic over Japan's crisis-hit nuclear plants, as callers flooded drug stores with requests for iodide pills.
As concerns over radiation deepened, crews boycotted ships bound for Japan, and Seoul started screening travellers from Japan and Japanese food for radiation.
Airport inspectors detected radiation from a Japanese man Thursday, but the level of radiation fell to normal after he removed his coat and took off his shoes, Yonhap news agency said.
South Korean officials moved to ease worries stressing that westerly winds would blow radiation from Fukushima, some 1,200 kilometres (750 miles) east of Seoul, out into the Pacific.
"Anxiety over radiation exposure is growing in this country following the explosion at Japan's nuclear power plants," the Korea Pharmaceutical Association said in a statement.
Drug stores were flooded with calls seeking to buy iodine, it said.
The association said iodide tablets could reduce the risk of thyroid cancer from radiation exposure but could also put users at risk of allergic reactions and problems with thyroid glands.
President Lee Myung-Bak called for a halt to spreading rumours over radiation exposure.
Police have launched a crackdown on text messages and social networking sites. On Thursday, they held a 28-year-old man in Seoul on suspicion of spreading rumours through an online messenger service.
Financial regulators are also investigating the source of a market rumour that exacerbated a stock market plunge on Tuesday. Those who cause confusion by spreading false rumours can be jailed for up to a year.
Foreign Minister Kim Sung-Hwan said South Koreans living within 80 kms (50 miles) of the Fukushima plant were advised to evacuate.
Korean Air plans to add up to five flights to its normal four flights per day between Wednesday and Sunday.
Second-largest Asiana Airlines said it had added one flight a day to its regular four from Narita to Incheon. It cancelled all flights to and from Fukushima.
Montenegro has called off a football friendly with South Korea scheduled for next week because of concerns over feared radiation fallout.
Source: AFP Global Edition