At least 23 people, including five women, were killed and 40 injured, when a three-storey residential building and two adjoining ones came crashing down following an explosion triggered by liquefied petroleum gas cylinders in Varachha area of Surat on Sunday, police said. 

The cylinders exploded at around 0325 IST on the ground floor of the building that housed a unit manufacturing 'sharan', an instrument widely used in diamond cutting, Additional Commissioner of Police Mohan Jha said.

Substandard material could have been used in the construction of the buildings, police suspect.

So far, 20 bodies have been extricated from the debris and sent for post mortem, he said.

A team of forensic experts is at the spot, but it will get a clear picture only after the debris is removed.

Asked if the police will file a first information report against the builder, Jha said, "At present we have only registered a case of accidental death. Only after receiving the forensic science laboratory report, any decision on action against the builder can be taken."

Rescue operations are on in full swing, he added.

Chief Minister Narendra Modi has announced compensation of Rs 50,000 to the kin of each of the deceased.