According to Portuguese media, the British officers will lower cameras on fibre-optic cables into the pipes this afternoon in a bid to find objects that may have been abandoned at the time.
Madeleine's parents Kate, 46, and Gerry, 45, are being kept informed throughout the excavation work. They are said to be bracing themselves for 'significant news'.
As part of Operation Grange, the force has made 287 requests for action to Portuguese legal authorities, which identify 41 priority areas of work.
It is not yet known what led them to the specific area in the coastal scrubland yesterday afternoon or what they found in the shaft.
They have just three more days of permitted time to finish digging around the coast, which they returned to yesterday, in the hope of finally solving the mystery of what happened to Madeleine.
The overgrown land - one of three key locations officers want to dig up - is the size of three football pitches and has been chosen because it is in the direction being taken by a suspect spotted carrying a little girl on the night Madeleine went missing.
Using chainsaws, picks and spades, officers have been conducting pains-taking searches of the scrubland just a five-minute walk from the Ocean Club apartments where Madeleine was last seen alive in May 2007.
Portuguese police pessimistic
Local newspaper Correio da Manha yesterday reported: "At this point in time, there's still no sign of the existence of human remains.
"The area marked off by the animals is now going to be subjected to more intense searches.
"Mechanical diggers are expected today."
While Scotland Yard refused to give a running commentary on the investigation, Portuguese police were said to be pessimistic about the potential findings.
Correio da Manha wrote: "The Policia Judiciaria have witnessed all the English police operations but they don't expect anything to come of them.
"For the PJ it's not credible that Madeleine's body is buried on the site or that remains will be found."
Earlier this week, specialist teams are thought to have used ground-penetrating radar equipment to look for disturbed earth.
The device uses radar pulses to take images of the subsurface of the ground. It can be used to check for disturbance in a variety of substances, including rock, soil, ice and fresh water. It can also be used to detect voids and cracks in buildings and under pavements.
The large area of scrubland, just a few minutes' walk from the holiday apartment Madeleine was staying in with her family, is bordered by villas and town houses with one section alongside a road.
The site is dominated by a large mound in the middle where police have been parking their vehicles and officers stand watch with binoculars, monitoring the movements of the scores of press gathered below.
As well as the small section of land the radar equipment was used in, officers also appear to be focusing on a flat area to one side of the slope, where soil samples have been taken.
Forestry workers continue to clear away undergrowth from the spot, using strimmers to aid the search. Officers have also been seen shovelling earth into buckets which has then been taken away for examination.
Small yellow marker flags poking out of the ground are being used to mark specific sites of interest while tape has been laid on the ground as police carry out their methodical search.
Dressed in Metropolitan Police uniforms, officers scoured the long grass on their hands and knees and collected soil samples, while being advised by forensic archaeologists and anthropologists from the UK.
Portuguese officers on horseback patrolled the area, while others had German shepherd dogs.
- Daily Mail
