Specialist ground-penetrating radar is now being used in the latest searches for missing Madeleine McCann.
Teams of German and Portuguese police officers, as well as firefighters, face the daunting task of hunting for evidence 18 years on from the disappearance of the British three-year-old in 2007.
Investigators scoured scrubland and abandoned buildings on the second day.
This week’s operation is focusing on a sparsely developed area of land around 3.5 miles from Praia da Luz, where Madeleine was last seen while on holiday with her parents and siblings.
Ground-penetrating radar was seen being used as work continued on Wednesday, amid intense international media scrutiny.
She vanished after she was left sleeping in a room with her toddler twin brother and sister while her parents went for dinner with friends in a nearby restaurant.
Kate and Gerry McCann are not commenting during the “active police investigation”, staff at the Find Madeleine Campaign said.
On Wednesday, officers were seen clearing vegetation around abandoned buildings, wearing protective gear such as hard hats and face masks, and a digger was used to move rubble.
The area where they are working is an area of fields and scrubland between a main road and the sea, with a few buildings including a vineyard.
It has been variously reported that teams will look where trenches were dug near the resort at the time of Madeleine’s disappearance, at wells, ruins and water tanks, and that there are plans to examine 21 pieces of land.
The search is being carried out at the request of the German federal police, as they look for evidence that could implicate prime suspect Christian Brueckner, who is in prison for raping a 72-year-old woman in Praia da Luz in 2005.
He is due to be released from jail in September if no further charges are brought.
In October last year, Brueckner was cleared by a German court of unrelated sexual offences, alleged to have taken place in Portugal between 2000 and 2017.
About 30 German police, including forensic experts, are expected to take part in the search alongside Portuguese officers. The operation is expected to last until Friday.
The Metropolitan Police said they were aware of the operation but that British officers will not be present.
German investigators and Portuguese officers last carried out searches in 2023, near the Barragem do Arade reservoir, about 30 miles from Praia da Luz.
Brueckner, who spent time in the area between 2000 and 2017, had photographs and videos of himself near the reservoir.
It was previously searched in 2008, when Portuguese lawyer Marcos Aragao Correia paid for specialist divers to search it, after he claimed to have been tipped off by criminal contacts that Madeleine’s body was there.
British police were later given permission to examine scrubland near where she vanished in 2014.
