A fire raced through a small South Korean hospital with no sprinkler system on Friday, killing 37 people, many of them elderly, and injuring more than 140 others in the country’s deadliest blaze in about a decade.

Sejong Hospital in the southeastern city of Miryang has a separate nursing ward where 94 elderly patients were being treated, but all of them were safely evacuated, fire officials said.

Most of the victims were on the first and second floors of the hospital’s six-story general ward, where its emergency room and intensive-care unit were located. Officials believe the fire started in the emergency room.

Mirayng police official Kim Han-su said 34 of the dead were women and 26 were in their 80s or older. He said police may be able to announce the cause of the fire on Saturday.

Police and forensic investigators dressed in white clothes, masks and helmets examined burned equipment in the blackened emergency room.

Dark smoke and flames were pouring from the emergency room when firefighters arrived, so they used ladders to enter second-floor windows. Some carried patients on their backs to other rescuers below, who moved them on stretchers to ambulances.

Several fabric escape chutes were hanging from the building’s sixth floor windows after being used to evacuate patients and hospital staff.

Dozens of fire trucks and two helicopters were sent to the hospital as thick smoke blanketed nearby streets. The blaze was extinguished in about three hours.

Three of the dead worked at the hospital — an emergency room doctor and a nurse and nurse assistant on the second floor — said Son Kyung-cheol, head of the foundation that operates the facility. The National Fire Agency said officials were trying to identify other victims.

Most of the deaths appeared to be due to suffocation, with only one victim suffering burns, a National Fire Agency official said on condition of anonymity because he wasn’t authorized to speak to the media.

Authorities said 143 people were injured, including seven who were in serious condition.

Son said the hospital did not have sprinklers because they were not required by law. Fire officials said the hospital wasn’t big enough to require them.

Fire official Choi Man-wu said authorities were investigating whether the hospital had missed any mandatory safety inspections, although Son said it had not.