The incident took place in the Russian-built Zvezda module and occurred as the station's batteries were being recharged.
Tetovo Mayor Teuta Arifi declared three days of mourning for the victims.
A psychiatrist recently recommended that he be forcibly medicated.
Police identified the man killed as Preston Spencer, 34, of Wichita.
"There was just metal, wood, debris, everywhere."
Fifteen prison officers guarding the cell block were unhurt.
The hospital had been caring for 56 patients, about half of them suffering from COVID-19.
Since Monday, the fires had grown by more than 20 square miles.
"They begged for their lives and I killed them anyway."
The dead were adults in their 50s and children who were apparently in the 10 to 13 age range.