There has been no contact with Julen Rosello since he fell down the narrow shaft, some 100 metres (350 feet) deep, on January 13 while playing as his parents prepared a picnic nearby in the southern town of Totalan near Malaga.
After abandoning an initial plan to reach the boy with an angled tunnel because of repeated collapses and landslides, workers installed a giant drilling machine on Saturday at the site to start digging a vertical tunnel parallel to the well, to a depth of 60 metres.
They reached this level on Monday evening, local daily Diario Sud reported.
But the shaft still needs to be reinforced to protect against landslides, which could take five to six hours, said rescue team engineer Juan Lopez Escobar.
Then a team of eight expert miners will be lowered down the shaft in a specially made cage to start digging a four-metre horizontal tunnel to the location where they believe the toddler is, another lengthy process.
The miners will dig the horizontal tunnel “with the help of a pickaxe if the ground is soft, otherwise we will employ tools used in the mining industry such as jackhammers and explosives,” Lopez Escobar said.
“You have to realise that in a few days we are carrying out an operation that usually takes months, without any geological study,” he added.
Hundreds of people, including specialised army and police units, are taking part in the unprecedented rescue operation, which is being closely followed by Spanish media.
Neighbours and family members of Julen's parents told Spanish media that the couple lost another child, Oliver, aged three, in 2017. The child had cardiac problems.
— lucia (@clhoe666) January 21, 2019
“I believe in God, I am sorry to say this but He has been very unfair to us,” Julen's grandmother told private television Antena 3 last week, adding that she believed Oliver was “protecting” Julen in the well.
Officers have questioned both parents and an entrepreneur who dug the well, a police spokesman said Saturday, adding that this was routine in such circumstances.
The well was unmarked at the time of the accident and regional authorities in Andalusia said the necessary permission had not been sought before it was dug.