At least 28 people were killed and 26 injured Thursday in a major blaze at a building housing a sports center and public bath in the South Korean city of Jecheon, officials said.
A Jecheon fire department official said the toll could rise as rescuers continue to search the building after putting out the fire. He spoke on condition of anonymity, citing office rules.
He said many of the people who died had been using a public bath on the second and third floors, which made it harder for them to escape.
The fire broke out around 4:00pm local time (0700 GMT) and quickly engulfed the entire eight-story building, leaving many trapped inside.
Sixteen victims were found at a public sauna and two elsewhere in the building, the National Fire Agency said.
"The fire produced so much toxic smoke so quickly, leaving many people unable to evacuate," the spokesman 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 building had several restaurants and leisure facilities, including a gym, the public bath and an indoor golf practice facility, the officials said.
Jecheon is in central South Korea, about 120 kilometers (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.
Organizers for the Pyeongchang Winter Olympics said the Olympic torch relay had been scheduled to pass through Jecheon on Friday, but the route has been revised as a result of the tragedy.