"Four people -- a woman and three men -- were killed. Another 22 people are in various hospitals," Poland's State Fire Service said.
The fire broke out at a hospice in the northern Polish city of Chojnice around 3 a.m. local time (0200 GMT), a spokesman for the fire brigade said, Xinhua news agency reported.
When the fire started, staff members and 23 patients were in the building. All the victims were patients.
The fire has been put out and rescuers are still working at the scene.
Initial findings showed that the fire was likely caused by a careless smoker, a police official told local TV broadcaster TVN24.