Police investigating the disappearance of Madeleine McCann are searching an allotment in Hanover, German prosecutors have told the BBC.
They confirmed it was related to the investigation into Christian B, a sex offender in prison in Germany, who is the main suspect in the case.
Work began at the site on Monday and is expected to continue until Wednesday.
Madeleine was three years old when she went missing while on holiday with her family in Portugal in 2007.
She disappeared from an apartment in Praia da Luz on the evening of 3 May 2007, while her parents were with friends at a nearby tapas bar.
Her disappearance sparked a huge police hunt across much of Europe.
Christian B, 43, was revealed as the main suspect in the case in June, as German and UK police made a fresh appeal for help 13 years after Madeleine disappeared.
He is believed to have been in the area where Madeleine was last seen while on holiday in the Algarve in Portugal.
Police said the suspect was regularly living in the Algarve between 1995 and 2007 and had jobs in the area, including in catering, but also committed burglaries in hotels and dealt drugs.
German prosecutors have previously said they have evidence that leads them to believe Christian B killed Madeleine, but it is not strong enough to take him to court.
Last month, the Metropolitan Police said the case remained a “missing persons” investigation in the UK because there was no “definitive evidence” as to whether Madeleine was alive or not.
However, German investigators have said they are assuming Madeleine is dead.
After the latest police appeal, Madeleine’s parents, Kate and Gerry McCann, said: “We will never give up hope of finding Madeleine alive, but whatever the outcome may be, we need to know as we need to find peace.”