Investigators said that an electric short circuit or a leaky gas pipe at a ground floor cafe was most likely the cause of the fire at the Bailey Road building late at night on Thursday.
On the ground floor, plastic pipes were used for gas transmission, which is illegal, said a member of a probe committee formed by the fire service after visiting the seven-storey Green Cozy Cottage Shopping Mall.
The bomb disposal team of the Counter Terrorism and Transnational Crime unit of police also visited the scene.
Its chief Rahmat Ullah Chowdhury said, "Power cables in the entire building are burnt. This usually happens when power lines short out and cause a fire."
"We had not seen any exploded gas tanks during the inspection. But some of the tanks must have leaked, causing the fire to spread rapidly. We are investigating, and maybe we will be able to give a clearer explanation later."
Health Minister Dr Samanta Lal Sen confirmed that at least 46 people were killed in the devastating fire in a commercial building at Bailey Road area in the capital on Thursday night.
"The death toll in the deadly inferno originated in a multi-storey commercial building in city's Bailey Road on Thursday night reached 46...even the condition of the injured people, now undergoing treatment at hospitals, are critical", he told journalists at Sheikh Hasina National Institute of Burn and Plastic Surgery.