SEJONG (Yonhap News) -- Provincial quarantine authorities began culling more than 20,000 poultry Friday after a preliminary test indicated a possible outbreak of avian influenza, with the agriculture ministry saying it may be of a highly pathogenic strain.

A suspected AI case was reported Thursday at a poultry farm in Gochang, located some 300 kilometers southwest of Seoul in North Jeolla Province.

A DNA test is currently under way to confirm the outbreak and its exact strain, according to an official from the Ministry of Agriculture, Food and Rural Affairs.

The ministry said the test was expected to confirm an outbreak of highly pathogenic AI.

"The initial test confirmed it is a H5N1 strain, and whether the strain is highly pathogenic will likely be determined later Friday," it said. "It is very likely to be determined as a highly pathogenic strain."

Later in the day, another suspected case was reported from a duck farm in Buan, a county adjacent to Gochang, the ministry said.

Quarantine officials confirmed the deaths of some 90 ducks in their on-site probe, and the remaining ducks are also showing bird flu symptoms, according to the ministry.

Determining the exact strain of AI is often crucial as highly pathogenic strains of AI may require additional quarantine measures than low pathogenic strains.

Confirmation of an AI outbreak would be followed by the immediate launch of intensive quarantine measures that will include a lockdown of all poultry and personnel at farms in affected areas.

The provincial government of North Jeolla decided to take pre-emptive measures and cull all of the more than 20,000 ducks on the farm that reported the suspected case, the official said.

The ministry said it has also began taking initial quarantine measures at 24 poultry farms in four provinces that have recently purchased ducks from the affected farm in Gochang.

South Korea last reported an outbreak of AI in late 2011, which led to the culling of over 3 million poultry.