The South Korean health authorities said on Wednesday that five individuals are now being tested on swine flu influenza amid a rising alert against the virus.

The Korea Centers for Disease Control and Prevention (KCDC) said in a statement that it is conducting tests on the five citizens, including a 15-month-old baby.

They have recently returned from trips to Mexico or the United States and they showed flu-like symptoms, the center said.

It was earlier reported that nine people had voluntarily visited local clinics for testing, four of whom later showed negative results.

The KCDC confirmed on Tuesday that a 51-year-old woman, who was previously suspected of carrying the swine flu virus, was infected with type-A influenza, which was the nation's first probable case of swine flu.

In addition, the KCDC on Tuesday raised the nation's disaster alert level by one notch to "Yello" from the previous "Blue" amid growing concerns over the spread of swine influenza around the world.

As of early Wednesday, a total of 236 people worldwide had been confirmed to carry the virus, with around 2,500 suspected cases reported.