Confirming a report in the daily "Kronen Zeitung," Walter Anzboeck said work has started and the basement should be filled with concrete in about two weeks.
Fritzl's daughter Elisabeth disappeared from the town of Amstetten in 1984 at age 18, re-emerging in 2008 from the dungeon-like basement chamber where her father had kept her captive.
A court found him guilty of raping her thousands of times. Of the seven children she bore him, one died in captivity after Josef Fritzl refused to allow medical treatment.
Josef Fritzl was sentenced to life in a prison psychiatric ward in March 2009. Elisabeth Fritzl and her children were given new identities.
No decision has been made public on whether the house will be torn down as advocated by some Amstetten residents, who fear their town will be forever linked to the Fritzl case.