The fire in the southern Bulgarian town of Sliven broke out at about 2:40 am, the chief of the local fire brigade, Vladimir Demirev, told reporters.
The blaze occurred in a room on the fourth floor where three male patients were receiving care.
“Two of the patients died on the spot, while the third one was transported to a emergency hospital where he has died of his severe burns,” Demirev said.
The fire was quickly extinguished, and an investigation was launched to establish the cause.
A new surge in coronavirus cases is overwhelming Bulgaria’s ailing health care system. On Sunday, health authorities reported 8,178 patients in COVID-19 wards, 745 of them in intensive care.
The Balkan country of 7 million remains the least-vaccinated in the 27-nation European Union, with less than one-third of its adults fully vaccinated.