South Korean health authorities are testing three people who have shown symptoms of the Zika virus as part of an ongoing effort to tighten quarantine measures and respond quickly to a possible outbreak, the government said Wednesday.

The Korea Centers for Disease Control and Prevention said it tested seven people for possible Zika virus infection, with four testing negative so far.

Detailed genetic testing carried out on the remaining three is ongoing with the results to be out later in the afternoon, it said.

"Tests are being carried out as a precaution, with very little chance that the three remaining people are infected," the KCDC said.

The Zika virus is transmitted by mosquitoes, which are not active during the winter months in South Korea, it said, adding people who have traveled to countries with Zika outbreaks could have been exposed.

Symptoms associated with the virus are fever, joint and muscle pain, a rash and headaches, with some having bloodshot eyes.

The virus is rarely fatal, but the World Health Organization declared it an international health hazard earlier in the week after it has been linked to causing serious birth defects.

Pregnant women with the Zika virus could deliver babies with microcephaly, or abnormally small heads and brains.

South Korea also placed the Zika virus on its National Infectious Disease list on Jan. 29, making it mandatory for doctors to report suspected cases. Failure to do so can lead to a 2 million won fine.

The government, meanwhile, held an emergency meeting of medical and quarantine experts on Tuesday and vowed to take all necessary measures so the country can be ready to counter the Zika virus. 

There are currently no vaccines available to treat Zika infections, with doctors advising patients to get rest and drink lots of fluid. (Yonhap)