The powerful blast caused a 5-meter-wide and 3.5-metre-deep hole in the road and damaged farm houses near the roadside.
Pieces of the truck were blown 100 meters away in the explosion, according to witnesses.
The driver was among the killed, state-run Xinhua news agency reported.
An old couple were injured after the explosion damaged the farmhouse they were in and have been sent to hospital, police said.
Investigators said they are yet to determine the cause of the explosion, though the truck was licenced to transport explosives.