At least 29 people were killed and 29 more were injured on Thursday in a major blaze at a building housing a sports centre and public bath in the South Korean city of Jecheon, officials said.
The fire broke out around 4:00pm local time (7am GMT) and quickly engulfed the entire eight-storey building, leaving many trapped inside.
Sixteen victims were found at a public sauna and two elsewhere in the building, the National Fire Agency said.
Television footage showed the building consumed by flames and issuing dark plumes of smoke, as several people stood waiting to be rescued from an outdoor terrace.
The fire - believed to have started in a parking lot on the first floor - has been mostly put out, but the death toll may rise further as firefighters continue to search the building, an agency spokesman said.
"The fire produced so much toxic smoke so quickly, leaving many people unable to evacuate," the spokesman said.
Jecheon is in central South Korea, about 120 kilometres (75 miles) southeast of the capital Seoul.
President Moon Jae-In expressed regret over the accident and urged officials "utmost efforts" for rescue and search operations, his office said.
The worst fire accident ever to hit the modern South Korea was an arson attack on a subway station in the southeastern city of Daegu that killed 192 people in 2003.