Almost 50 Kamen residents had to leave their houses in the Ruhr region after the ground collapsed around a construction site where an excavator was drilling for a geothermal heat pump, a natural heating source for houses and water. The crash left a funnel-shaped hole with a diametre of 10 metres and four metres deep and destabilised the surrounding area.
Authorities evacuated the area when cracks in the ground appeared.
Residents left their homes safely and no one involved in the mining accident was injured.
Two houses are still in danger of collapsing as the surrounding earth drops at a rate of two centimetres an hour, a fire department spokesman said in a statement Friday morning. While the ground is now stable, houses within a 300-metre radius of the hole remain empty, he said.
It remains unclear how many people have been allowed to return to their homes.
Heavy equipment frequently causes old, unfilled mine pits to collapse in the Ruhr region after decades of heavy mining.