SEOUL (REUTERS) - South Korea will mobilise military forces in the capital Seoul to help frontline health workers deal with a surge in coronavirus, with 689 new cases reported on Friday (Dec 11), and as the death toll and number of patients in critical care rose.

Of the new cases, 673 were locally transmitted, which brings the total tally to 40,786, the Korea Disease Control and Prevention Agency (KDCA) said. The death toll increased by eight to 572 deaths, KDCA reported.

The surge in cases has delivered a blow to South Korea's vaunted pandemic-fighting system which successfully used invasive tracing, testing and quarantine to avoid lockdowns and blunt previous waves, and keep infections below 50 per day for much of the summer.

The authorities scrambled to build hospital beds in shipping containers this week to ease strains on medical facilities stretched by the latest coronavirus wave.

The number of patients in serious or severe conditions have grown near 170, prompting the health authorities to seek more beds nationwide.

Calling the current wave a critical crisis, Prime Minister Chung Sye-kyun said he will dispatch around 800 military, police and government workers in every district of the greater Seoul area to help track down potential patients.

Frontline workers and medical staff are struggling each day to conduct endless epidemiological investigations, testing and securing insufficient beds, as the confirmed cases grow in various areas including the metropolitan Seoul area, Chung told a government meeting on Friday.

"In the end, in order to tamp down this wave, it is key to seize the victory in virus-prevention efforts in the greater Seoul area," said Mr Chung.

The majority of the new cases have been reported in the capital city of Seoul, the neighbouring port city of Incheon, and Gyeonggi Province, which is home to 13.5 million people and surrounds both cities.