A six-year-old child died in a fire in an apartment building in Hamelin in Lower Saxony.
The 27-year-old father and two other children of the family of seven are in mortal danger, a police spokesman said on Sunday.
The 23-year-old mother and the other two children were also treated in hospitals.
The fire broke out on Saturday afternoon for reasons that are still unknown.
As soon as they arrived, the firefighters saw massive smoke rising from an apartment in the apartment building, the operations manager said on Saturday.
Some residents stood at the window, whereupon first responders tried to rescue them from the house with a ladder.
Some of the residents of the house near downtown Hamelin were brought out of the house with the help of the fire department.
According to the police, the children were between almost a year and six years old, the oldest succumbed to his serious injuries in the hospital.
Five rescue helicopters were in use, the fire brigade with around 70 emergency services on site.