Three men died when a fire broke out in a COVID-19 ward of a hospital in the southern Bulgarian city of Sliven early on Sunday, officials said.

The fire, which was quickly extinguished, broke out at around 0040 GMT and affected one room. Six patients in adjacent rooms were moved to other hospital wards, the head of the regional fire safety department Vladimir Demirev said.

Two of the men were found dead by firefighters. The other patient suffered heavy burns and was transported to another hospital, where he later died.

The cause of the fire is being investigated, but a cigarette lit by a patient was the most probable cause of the fire, the health ministry said in a statement.