For the first time since the Cold War the German government is advising citizens to stockpile food and water for use in a national emergency.
Some opposition MPs said the new civil defence concept, to go before ministers on Wednesday, was scaremongering.
Citizens are advised to store enough food to last them 10 days, because initially a disaster might put national emergency services beyond reach.
Five days' water - two litres (half a gallon) per person daily - is advised.
The German news website Frankfurter Allgemeine (FAZ) said the new concept was set out in a 69-page German Interior Ministry document.
The document said "an attack on German territory, requiring conventional defence of the nation, is unlikely". But, it said, a major security threat to the nation in future could not be ruled out, so civil defence measures were necessary.
Soon, Germans began tweeting ironically under the hashtag "Hamsterkaeufe" (panic-buying).
Interior Minister Thomas de Maiziere told a group of schoolchildren that Germany must be prepared to react if water or food reserves were poisoned, or if oil and gas supplies were interrupted.
The parliamentary head of the left-wing Die Linke party, Dietmar Bartsch, criticised the move, saying "you can completely unsettle people with yet another round of proposals, such as hoarding supplies".
The Greens' deputy parliamentary leader, Konstantin von Notz, said it was sensible to update civil defence advice which had not been touched since 1995.
But he warned against mixing up possible military or terrorist scenarios, saying "I can't see any attack scenario that merits a stockpiling of supplies by the population".
Germany's civil defence: Cold War and now
- About 2,000 public bunkers and shelters were built in West Germany, with federal funding (former East Germany had its own communist network of shelters)
- There was a wide mix of shelters - eg in garages, schools, private cellars
- Special government nuclear bunker was built in Bad Neuenahr-Ahrweiler, 30km (19 miles) from Bonn
- Law says Cold War-era shelters must not be converted into new types of building
- Germany still has stockpiles of food - eg milk powder and beans - at secret locations, for a national emergency
- Inventories are regularly checked and renewed
- Emergency offices to issue food and fuel stamps, under national rationing system in a disaster