Major South Korean corn processors have begun importing genetically modified varieties of the crop because of shortages of conventional corn on the world market since China began limiting its exports, officials said Friday.

About 63,000 tons of genetically modified U.S. corn arrived in South Korea on Thursday, the first large-scale imports for human consumption since the government began regulating biotech crops in 2001.

Four major South Korean companies, which make up about 90 percent of the corn processing market, had refrained from importing such corn because of negative perceptions among consumers of genetically modified organisms, or GMOs.

But now they say they cannot help but import GMO corn.

"China has stopped exports, while European countries are sweeping off non-GMO corn from Latin American nations," said Yoo Chang-kyu, an official with the Korea Corn Processing Association, the business lobby for the four companies. "We don't have any other options."

The companies use corn to produce corn starch, a key ingredient in cookies, beverages, ice cream and other foods.

Environmental and consumer groups protested the import of biotech corn, calling it "monster food."

"The safety of genetically modified corn has not been fully verified," they said in a joint statement. "If food is made with it, the health of our nation's people can be threatened."

On Thursday, activists held a protest at the port of Ulsan, where the GMO corn arrived, Yonhap news agency reported.

South Korea imported about 10.5 million tons of corn last year, with 8.2 million tons intended for animal feed and 2.3 million tons for human consumption, according to the Agriculture Ministry.

About half of the amount for human consumption was imported from China, 30 percent from the United States and the remainder from Brazil and other Latin American nations, it said.

China began limiting corn exports last year to avoid domestic shortages.

Local newspapers said the four Korean companies are expected to import about 1.3 million tons of GMO corn this year.

But Yoo, of the corn processing association, said the amount is likely to be less than that considering the expected backlash from consumers. He provided no exact estimate.

Yoo said the price of non-GMO corn has more than doubled to about US$360 per ton since 2006.

South Korea enforced a regulation in 2001 that calls for the labeling of products that contain GMOs.

Although no GMO corn had been imported in large amounts since then, about 70 percent of the country's soybean imports are genetically modified, according to the Korea Food and Drug Administration.