Under the impact an entire wall on one side of the single-storied house, built for an Anganwadi centre in Nowapara locality of the area, caved in, Birbhum district SP Mukesh told PTI.
The bombs exploded between 2AM to 2.30AM, he said.
"The blast happened inside an Anganwadi building which is yet to become functional. Nobody has been injured in the blast," the SP said.
On how the bombs reached the building, the IPS said, "That's quite surprising. We believe that because the building was vacant somebody must have kept them there. We are ascertaining how many bombs were actually kept there. Our senior officers are carrying out an investigation."
The area is also considered a political turf of supremacy between the ruling Trinamool Congress and CPI(M).