BERLIN (AP) — Three patients were killed and many people were injured in a fire that broke out overnight at a hospital in the German city of Hamburg, authorities said Sunday.

Firefighters were alerted to the blaze at the hospital, the Marienkrankenhaus, shortly after midnight. It broke out in a room in the geriatric ward, on the ground floor of the building, and spread to the facade of the floor above. Smoke spread across the building's four floors, German news agency dpa reported.

It wasn't immediately clear what caused the fire and police said results of the investigation weren't expected on Sunday.

The three people who died were men aged 84, 85 and 87, police said in a statement. Another 34 people were injured, one of whom was in a life-threatening condition.

A section of the hospital had to be evacuated. Injured patients were treated mostly at the hospital itself, though two were taken to nearby clinics. The fire was extinguished within about 20 minutes.

Firefighters said they found several patients at the windows calling for help. People were rescued using ladders and through the building itself.