The blast, which happened just before 9am on Friday morning, has left two people injured, one seriously. Police are still looking for a further missing person, and have brought in the help of sniffer dogs and a heat sensing camera mounted on a drone according to Ruhrnachrichten.
The fire brigade also brought in a device which picks up potential knocking that cannot be picked up by the human ear, but the work is being made more difficult as the building is at risk of collapsing.
It is still not clear whether the missing person was in the house at the time of the explosion, according to a police spokesperson.
The power of the blast destroyed the attic and both of the two upper floors of the building in the district of Hörde.
Tonnes of debris was thrown onto the street, but no pedestrians were injured. Two witnesses are still suffering from shock, according to the fire brigade.
According to the Ruhrnachrichten, the police visited the flat on Thursday night. Neighbours told reporters of an inhabitant of the apartment building running riot, prompting police to be called.
Residents also said that the man was psychologically unstable, and that there are often arguments and police involvement. The man was supposedly recently told he was going to be evicted from his flat next week.
Police say it is unclear whether this has anything to do with the explosion. They have also not said how the explosion happened.