After days of complications, the vertical tunnel that miners are using to rescue two-year-old Julen in Totalán was finally ready for the next stage of the operation on Thursday.
After final safety checks the first pair of miners were lowered inside the shaft on Thursday afternoon.
After the completion of an access platform on the surface, the specialists from the Asturias Mining Rescue Brigade are working at the bottom of the shaft in order to tunnel through three metres to the reach the boy.
Julen fell down a 100-metre-deep borehole on Sunday 13 January and the rescue operation has take the form of an unprecedented feat of emergency engineering.
A vertical tunnel, drilled parallel to the original hole the boy fell down, had to be lined by metal tubing before the miners could go down in a specially made capsule to start digging.
The uneven surface of the tunnel walls, however meant that the tubes came up against two obstructions which had to be dealt with.
Engineers found that the wall of the tunnel that was completed on Monday night had an obstruction at a depth of 40 metres. The shaft was eventually widened and its walls smoothed, and the tubing began to be inserted again early on Wednesday morning.
Later on Wednesday, however, at a depth of 50 metres, the tubing came up against another obstruction, a rock protruding from the tunnel wall.
A team of solderers was called in to reduce the size of the final ten metres of tubing.
Monday's work had also come across setbacks after the machinery came across a layer of especially hard rock at a depth of 52 metres, slowing down progress. The drilling of the parallel tunnels started 25 metres below the top of the original hole thanks to excavations into the hillside. At a depth of 60 metres the miners were due to start their work.
This is the first time in Spain that a tunnel of this size has been dug to a depth of 60 metres.
Around 300 experts have been working round the clock in the Sierra de Totalán on this complex rescue operation.
Julen fell into the hole, which is just 25 centimetres wide, while his family were spending the afternoon in the rural area near the Cerro de la Corona dolmen.
Since the start of the operation, three possible approaches had been considered: to clear the earth which had trapped Julen in the original hole; build a parallel shaft (wide enough for a human) then connect the two; or build a connecting perpendicular tunnel. However, the first and last options were discarded with the former increasing the risk of further earth falling in and the latter expected to take much too long, given the instability of the terrain.
By Thursday last week, all efforts concentrated on digging the parallel hole which "in normal circumstances would take a month", according to Juan López Escobar, spokesman for the Colegio de Minas in Malaga.
"To put a timescale on it now would be reckless," he added. "We are working to do it as quickly as possible but we're talking days rather than hours."