The boy fell into the borewell around 5.30 p.m. on Friday and got stuck at 30-ft and rescue efforts began soon after that.
Later that night, he fell further down to about 90 ft.
Speaking to reporters, Tamil Nadu Health Minister C. Vijaya Baskar said: "The rig deployed to dig a hole near the borewell has gone to a depth of only about 40 ft owing to the rocky terrain."
He said the next course of action will be taken after discussions with different organisations.
"The rescue efforts will not be abandoned. The rocky terrain prevents faster boring. The rig is drilling about 280-500 cm per hour," J.Radhakrishnan, Principal Secretary, Revenue Administration, Disaster Management and Mitigation department told reporters.
Radhakrishnan said, it may take about 12 hours to dig about 100 ft. After that a horizontal tunnel will be burrowed to get to the borewell to reach the boy.
He said, it was initially estimated that drilling the new hole would be completed in 6-10 hours.
Radhakrishnan said experts with technologies that may be deployed to rescue the boy are welcome.
"Support is being provided to the boy's parents. They should not start feeling guilty for the boy's present condition," Radhakrishan said.
According to reports, stronger blades that can break rocks are being sent from Chennai to be fitted in the rig.
On Saturday, the National Disaster Response Force (NDRF) and State Disaster Response Force (SDRF) took over the rescue operation as other techniques used to take the boy out of the borewell have failed.
Initially, earthmoving equipment was pressed into service to dig a pit near the borewell to reach the boy. But, it was stopped midway as the terrain was rocky. Besides, it was felt that this process could cause vibrations that may loosen the soil inside the borewell, thereby slipping the boy further down.
Later, the rescue team used a special equipment 'borewell robot'. But that too was not successful.
Several teams with their own technologies have tried to rescue the boy, but all that has so far failed.
( With inputs from IANS )