Police have identified the dead as Muniraju (10), son of Narayanappa and Vajramma, residents of Chikkondahalli.
Police suspect that the boy must have drowned in the murky water of the tank which was about 20-ft deep.
A fire brigade and trained swimmers from Hosur in Tamil Nadu have been called to recovery the body.
In spite of massive efforts, the body could not be traced till Thursday evening, police said.