The fire started around 7:30 am local time at the rear of the emergency room on the first floor of Sejong Hospital and it was mostly extinguished after a few hours, Choi Man-woo, the head of Miryang city's fire station, told a televised media briefing.
Firefighters were still in the process of evacuating around roughly 200 people from the main hospital building and nursing home directly behind the hospital, Choi said.
At of the time of the briefing, Choi said 10 people had been critically injured and 35 slightly injured.
Local news channel YTN showed black smoke billowing from the windows and entrance to the hospital and flames flickering.
Miryang is about 270 km southeast of the capital Seoul, and the people evacuated were being treated at four other hospitals nearby, YTN said.
The fire comes just a month after 29 people died in a blaze at an eight-storey fitness centre in Jecheon City.