South Korea's daily coronavirus caseload spiked to a two-week high on Wednesday amid growing concerns over the threat posed by variants that have been spreading around the world.

The Korea Disease Control and Prevention Agency confirmed 645 new infections in the last 24 hours, bringing the overall case total to 152,545.

The death toll rose to 2,007.

For the fourth day in a row, the KDCA reported over 40 new imported cases.

Although the number of new infections usually rises mid-week on the back of increased testing, health authorities have expressed worry about a potential surge in COVID-19 cases involving variants, especially the more transmissible Delta variant that was first detected in India.

The country has yet to report a large number of the Delta variant cases, but officials said it's still too early to make assumptions.

They said the mass vaccination program is the best countermeasure.

More than 15 million people, or just over 29 percent of the country's 52 million population, have received their first shots of COVID-19 vaccines.

More than 4 million people were fully vaccinated as of Wednesday.