"It was like a giant New Year's firework," Iselin Målvatn, who was in the area when the truck exploded, told VG newspaper. "It was totally sick. We saw the smoke and felt the pressure as we sat in the car."
Police evacuated the area after the truck caught fire early in the afternoon, creating a 1000m exclusion zone around the vehicle and clearing residents from nearby houses.
"All construction workers have been evacuated," Egil Pettersen from the Helgeland police told VG newspaper before the blast. "Now we are checking if any of those who live in houses in the area are home."
The driver of the truck escaped as soon as he realised his engine had caught fire, and is unhurt.
The truck was bringing explosives into a quarry in Ømmervassveien, between Ømmervatn and Drevja in Nordland county.