The number of new coronavirus infections linked to a call center in southwestern Seoul has reached 90 cases, the capital's mayor said Wednesday, spawning concerns about potential mass transmission in the metropolitan area.

"The 90 cases come from (virus tests of) 207 employees who worked on the 11th floor and their families," Mayor Park Won-soon told a radio show, "A total of 550 call center workers on other floors of the same building are being screened."

Among the cases, Seoul accounted for the highest number of infections with 62 patients, followed by 15 in Incheon, west of Seoul, and 13 in Gyeonggi Province, according to Park.

The call center infection is so far the biggest COVID-19 infection cluster in Seoul, which is home to 10 million people.

When including the nearby Gyeonggi Province and Incheon, the case poses a potential risk to the wider metropolitan area's population of 25 million.

Park said that two out of the 207 workers of the call center in the Shindorim neighborhood were found to be followers of the fringe religious sect Shincheonji, which is associated with more than 60 percent of South Korea's total infections.

The two workers have so far tested negative, but Park said the city government will look into the case for possible links.

According to government figures from midnight Monday, South Korea has reported 7,513 infections since its first confirmed case on Jan. 20.

Cases in Seoul had reached 156 by 10 a.m. Tuesday, according to the city government's separate data. (Yonhap)