The rescue effort began on Sunday and went on through the night
The search began on Sunday afternoon and continued at night near Totalán, a village in hills north-east of Málaga.
They do not know if the boy is still alive. A camera lowered into the well found his bag of sweets and a plastic cup 78m down, Spanish media report.
Firefighters and police inserted tubing to shore up the well, dug to get water.
They are still trying to work out how best to get the two-year-old, named by media only as Yulen, out.
Nobody can squeeze down the narrow shaft, so the plan is to drill a parallel tunnel, but rescuers must avoid knocking the borehole's earthen sides.
The boy's father rang police at 14:00 local time (13:00 GMT) on Sunday to tell them Yulen had fallen into the well.
Guardia Civil police joined dozens of firefighters with equipment designed for such tight spaces