South Korea has reported its largest daily increase in coronavirus infections on Christmas Day, as the prime minister pleaded for vigilance to arrest a viral surge that has worsened hospitalisation and deaths.

The 1,241 new cases confirmed by the Korea Disease Control and Prevention Agency brought the country's caseload to 54,770. Seventeen Covid-19 patients died in the past 24 hours, bringing the death toll to 773.

More than 870 of the new cases were from the greater capital area, home to half of the country's 51 million population, where more than 500 infections have been linked to a huge prison in Seoul. Clusters have been popping up from just about everywhere in recent weeks, including hospitals, long-term care facilities, churches, restaurants and army units, according to AP.

The country has been expanding its mass testing programme to slow the rate of transmissions and more than 118,000 tests were conducted on Thursday alone.