About one million dollars has been stolen in Poland from a convoy transporting the money in the south-west.
The money disappeared as five security guards were taking it from Wroclaw to Poznan in the west.
Police are considering the possibility that some of the guards may be involved.
Polish television described it as the robbery of the century, and said the sum involved was greater than all the money taken in bank robberies in the country this decade.
From the newsroom of the BBC World Service
Country profiles
Violence greets Clinton visit
Russian forces pound Grozny
EU fraud: a billion dollar bill
Next steps for peace
Cardinal may face loan-shark charges
Vodafone takeover battle heats up
(From Business)
Trans-Turkish pipeline deal signed
French party seeks new leader
Jube tube debut
Athens riots for Clinton visit
UN envoy discusses Chechnya in Moscow
Solana new Western European Union chief
Moldova's PM-designate withdraws
Chechen government welcomes summit
In pictures: Clinton's violent welcome
Georgia protests over Russian 'attack'
UN chief: No Chechen 'catastrophe'
New arms control treaty for Europe
Mannesmann fights back
(From Business)
EU fraud -- a billion-dollar bill
New moves in Spain's terror scandal
EU allows labelling of British beef
UN seeks more security in Chechnya
Athens riots for Clinton visit
Russia's media war over Chechnya
Homeless suffer as quake toll rises
Analysis: East-West relations must shift