SEOUL, May 28 -- At least 21 people were killed and eight others injured in a fire that occurred at a sanatorium in Jangseong, some 300 kms south of the South Korean capital city of Seoul, early on Wednesday, local broadcaster YTN reported.

The fire started at an empty sickroom in the far right side of the sanatorium's annex building, and hadn't moved to the main building as the passage linking the two is in the far left of the annex building.

The fire, which broke out at 00:27 a.m. local time, was put out in less than 30 minutes. The initial fire was brought under control in just six minutes, and put out completely in 28 minutes.

But the nursing home had scores of old patients who have problems with mobility, contributing to the rise in the death toll.

When the fire broke out, a total of 324 patients were in the sanatorium where 15 nurses and nurse aides were on duty.

The auxiliary building accommodated 34 patients, mostly in their 70s to 90s bedridden for Alzheimer's disease, stroke and other diseases. At that time, only one nurse and one nurse assistant were on duty.

The dead included 20 patients and one nurse aide. All the dead were suffocated by poisonous gas.

Among the wounded, six people sustained serious injury, boosting fears for a gain in the death toll. Two suffered a minor injury.

The fire was believed to have been caused by a short circuit as there were no inflammables in the patient room where the fire started. Police and fire department officials were under investigation.

Firefighters said some patients had their hands tied to the sickbed, contributing to the increase in casualties, but the sanatorium denied it.

The accident came two days after seven people were dead and 58 others wounded in a fire at a bus terminal in Goyang, a city northwest of Seoul.