South Korea has reported its first cases of the Omicron coronavirus variant and tightened travel restrictions as fears grow about the strain's impact on the country's ongoing Covid surge, reports AFP.

Health authorities said Omicron has been detected in five people, including a fully vaccinated couple who had visited Nigeria from November 14 to 23, returning two days before the variant was officially reported by South Africa.

They tested positive for the coronavirus on Thursday, and subsequent genetic sequencing tests showed it was the new variant, said the Korea Disease Control and Prevention Agency. It said their friend also had Omicron.