German businesses are being advised by the army on how to cope in the event of war breaking out with Russia.

A secretive 1,000-page document, named Operations Plan Germany, contains tips for businesses on how to keep operations running smoothly in wartime, such as preparing replacement staff for migrant workers who leave the country.

It also lists key commercial buildings and other infrastructure that would need to be protected by the German army and broad logistical plans for hosting tens of thousands of allied Nato troops on German soil.

The document has been kept under wraps but a rough outline of its contents was disclosed to the German news outlet Frankfurter Allgemeine Zeitung.