Several other people were injured in the crash, with four being rushed to hospital.
The extent of the victims' injuries remains unknown. The driver of the train, however, escaped from the crash uninjured.
"I've experienced a train running into a wild animal before, but this crash was something different," passenger Nader Elselawy told the TT news agency, explaining that he felt a blast of air that forced his entire body backwards.
"I even felt it inside my chest," he said.
"You could hear breaking glass and see how some people fell over."
IN PICTURES: Click here to see images from the crash
Two carriages derailed as a result of the accident, which took place around midday at a level crossing outside Forserum on the rail line connecting Jönköping and Nässjö in south central Sweden known as the Krösatågen line.
The truck involved in the accident was carrying a digging machine.
"Apparently it was the arm of the digging machine that hit the engine, but I'm not sure exactly how it happened. But it was violent enough to cause serious damage to the front of the train," country transit official Jan Peter Pettersson told the TT news agency.
The crossing where the accident occurred lacks sound and light signals.
"It's a small branch road and the crossing over the railroad tracks is completely unguarded," Jan Lagerqvist of the Jönköping police told TT.
Uninjured passengers have been taken to a meeting place where buses have been enlisted to take them to their final destinations.
Police expect the road to be closed for an extended period of time in order to allow officials to investigate the cause of the crash and clear the wreckage from the scene.