Authorities said most of the casualties were patients, according to the Yonhap news agency. Thirty-eight injured people were being treated at nearby clinics.
According to local media, the death toll from the devastating fire has gone up to 41.
Earlier, South Korean President Moon Jae-in has called an emergency meeting as death toll from the fire continued to rise reaching 33 from earlier reported 31.
The injured toll has also risen from 40 to 79 with 9 of them in critical condition, Yonhap reported.
A hundred patients were believed to have been trapped inside the burning building, the outlet said, with more than 90 residents of an adjoining nursing home evacuated right away.
Authorities reported that the fire suspected to have started in the emergency room of the main building of Sejong hospital.