The Foreign Office admitted a serious breach of security took place after blank passports destined for British embassies were stolen.
A spokeswoman said 24 parcels containing blank passports and vignettes - the blank stickers for visa stamps - were taken from a van en-route from a factory in Oldham to RAF Northolt near London.
It was reported 3,000 documents were stolen, but the spokeswoman was unable to confirm this number.
She said the incident was being investigated by Greater Manchester Police, adding the Home Office and Identity and Passport Service (IPS) had taken "preventative action" to guard against forgeries.
The Foreign Office spokeswoman said: "The van was hijacked en route from the production site."
She confirmed that the documents had been produced at Oldham-based printing firm 3M Security Printing and Systems, adding that they contained "security features" which would make them unusable.
BBC Radio 5 Live said the passports involved were the new electronic type which contain a chip replicating the data printed on the document itself.
An Identity and Passport Service spokesman said in a statement: "Our hi-tech security features mean that these passports are unusable.
"The police are doing everything in their power to catch the perpetrators."
Such sensitive documents are usually transported in armoured, secure vehicles, he added.
