Three members of a family were missing after an explosion collapsed a home in the western German city of Bruehl on Saturday, dpa reported.
A 12-year-old boy was rescued with injuries from the home, but his sister, father and the father's companion remained missing, the fire department said.
The explosion which brought down the semi-detached house was originally blamed on gas, but authorities have not been able to find any gas.
Investigations were continuing into the incident. Mayor Michael Kreuzberg said it was probably an accident, but that nothing had been ruled out.
"So far it has been practically impossible to analyse the situation due to the unstable conditions," he said, adding "We haven't given up hope" of finding more survivors.