As Libya descends into chaos, some heavily armed groups are getting exceedingly rich on banditry.
A daylight robbery on Monday saw $55 million stolen from the country's central bank.
The government van was intercepted by 10 gunmen when it left the airport in Sirte after arriving from Tripoli, a Libyan security official told the Associated Press on condition of anonymity. Despite containing millions of dollars, euros and dinars, the van had no security accompanying it, he said.
The army surrounded the city's main exits in an attempt to apprehend the thieves, Libya's official news agency reported, but there was no news of any arrests.
The attack is another example of the decreasing security situation in the country.
It is also another blow to Prime Minister Ali Zeidan, whose government is struggling to provide stability in a country flooded with weapons and militias.
Sirte, the hometown of former dictator Muammar Gaddafi, is particularly dangerous as Islamist militant groups and militias have pushed out the national army.
The five were protesting the 2011 assassination of former army chief Abdel-Fatah Younis, who switched to the rebel side during the uprising against Gaddafi's government.