Prosecutors said the two-day search in Hanover was linked to a murder investigation against a 43-year-old man but could not comment further.
Madeleine was three when she went missing while on holiday with her family in Praia da Luz, Portugal, on May 3 2007.
Advertisement
German investigators believe Christian Brueckner killed her soon after abducting her from a holiday apartment in the resort.
Brueckner is in jail in Germany for drug dealing, and is appealing against a conviction for the 2005 rape of a 72-year-old woman, also at Praia da Luz.
Newspaper Bild reported the foundations of a garden house were found on the site and, among the remains, a hidden cellar room was found.
