DURHAM, N.C. – One patient was killed and three employees injured in a fire early Tuesday at a long-term care unit occupying leased space at a North Carolina hospital, authorities said.

Firefighters were called to a report of an explosion on the sixth floor of Durham Regional Hospital about 2:15 a.m. Tuesday, said Durham Fire Department spokeswoman Sierra Jackson. Firefighters discovered there had been no explosion and the fire had been extinguished by the hospital sprinkler system.

Hospital officials were investigating exactly how the fire occurred and just where it began, said Katie Galbraith, hospital chief of operations. The sprinkler system caused water damage to the sixth floor, so other patients at the 30-bed Select Specialty unit were transferred to Durham Regional Hospital, said Kellie Peacock, Durham Regional's marketing director.