Two people burned in fire caused by the blast.
District police superintendent Moinul Haque said nature of the blast indicated it might be a bomb. A bomb disposal unit was staying at the scene and the members were searching the building.
The blast caused collapse of west side wall of the building which fell over the roof of a tin-shed house beside it. As a result the house was set on fire; however, fire service managed to douse the blaze.
Ibrahim, 22, son of tin-shed house owner Abul Khayer and brother in-law Ainal, 26, were injured in the fire and they were rushed to Dhaka Medical College and Hospital.
On information, police and Rapid Action Battalion members cordoned off the building owned by a Kuwait expatriate.
Abul Khayer, caretaker Shariful Islam and his wife Nargis Begum were held for interrogation, superintendent Moinul added.
Details of the incident will be described later, he said.