While callers flooded drug stores with requests for iodide pills, South Korean pharmacists issued an appeal Thursday cautioning against panic over Japan's crisis-hit nuclear plants.
Fears over possible radiation has spread across the Internet, prompting Seoul to launch a crackdown on scaremongering, with officials insisting that westerly winds will blow radiation 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.
The association said iodide tables 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.
"As there is little possibility of radioactive dust reaching the country, heavy doses of iodide needed to fend off radiation impact would only bring about health hazards," it added.
Fears over radiation deepened on Thursday as Seoul started screening travellers from Japan and Japanese food for radiation.
South Korean police on Wednesday launched a crackdown on spreading false alarms through text messages and social networking sites that radioactive materials would soon reach the Korean peninsula.
The Financial Supervisory Service watchdog is investigating the source of a rumour doing the rounds in the markets which exacerbated a stock market plunge on Tuesday.
In South Korea, those who cause confusion by spreading false rumours can be jailed for up to a year.
Aviation companies said Thursday that flights from Tokyo were fully booked as growing numbers of South Koreans joined the exodus from quake-hit Japan.
South Korea's largest airline, Korean Air, said it had "drastically" increased flights linking Tokyo's Narita airport and Seoul's Incheon airport.
It plans to add three to five flights to its normal four flights per day, to carry an additional 5,000 passengers between Wednesday and Sunday, a Korean Air spokesman said.
Asiana Airlines, the second largest South Korean airline, said it had added one flight a day to its regular four from Narita to Incheon.
It cancelled all flights to and from Fukushima for fears over radiation fallout after it closed the routes to the tsunami-hit Sendai City and Ibaraki Prefecture.
The Korea Football Association said Thursday that Montenegro had called off a football friendly with South Korea scheduled for next week because of concerns over feared radiation fallout.
"Players, their relatives and clubs opposed the visit to Seoul because of the quake and radiation leaks," it said in a statement.