The thieves struck while the German-registered vehicle was stationary at a petrol station near Rydebäck and the Estonian driver was sleeping in the cabin.
The truck contained ammunition and empty casings from Germany which were being taken to Estonia. The driver woke and saw the robbers escape in a silver-grey Volkswagen Transporter.
According to the driver there were four people.
Several police units joined the hunt for the thieves but by the middle of Saturday afternoon had no leads.
Hans Nilsson, a spokesman for Skåne police, told TT that the men got away with around 4,000 nine-millimetre cartridges, ammunition which can be used in pistols and submachine guns. An unknown quantity of cartridges of other calibres was also stolen.
Live ammunition is classed as dangerous goods, class 1, for which there are special regulations for road transport, including the training of drivers, marking vehicles with an orange sign together with stickers describing the type of goods.
Helsingborg police have not yet confirmed whether all of these rules were being followed.
There are also rules governing how a vehicle carrying such goods should be parked, either in a cordoned-off area or under supervision.
“But it isn’t easy for drivers to find such places on our roads,” said Bo Zetterström at the Swedish Rescue Services Agency in Karlstad.