Gunmen stole €39m in a robbery on a van carrying local and foreign currency for the Libyan central bank.
Ten armed men stopped the van in the coastal city of Sirte carrying 53 million Libyan dinars (€31m) and foreign currency worth €8.7m.
The van was coming from the airport where the cash had been flown in from Tripoli for the local central bank branch.
Head of Sirte council Abdel-Fattah Mohammed "The robbing is a catastrophe not just for Sirte but the whole of Libya," Abdel-Fattah Mohammed told Reuters.
He said the local authority had asked several times for better security for such transports.
The Libyan government has been struggling since the 2011 ouster of Muammar Gaddafi to assert control of a country brimming with armed militias, gangs and radical Islamists.
The OPEC country's oil exports fell to less than 10% of capacity today after protesters shut down ports and oilfields in the west.
Similar strikes over pay or political demands have already paralysed most of the eastern oil ports.