Photo taken on Aug. 23, 2018 shows the explosion site in Vietnam's northern Cao Bang province. Three workers were killed and another one injured in an explosion when they were preparing dynamite for the repair of a provincial road in Vietnam's northern Cao Bang province, Vietnam News Agency reported on Thursday. (Xinhua/VNA)

HANOI, Aug. 23 (Xinhua) -- Three workers were killed and another one injured in an explosion when they were preparing dynamite for the repair of a provincial road in Vietnam's northern Cao Bang province, Vietnam News Agency reported on Thursday.

All the three victims aged 35, 28 and 21, and the injured man aged 22 lived in Cao Bang's Thong Nong district and worked for a local construction company in the same district.

When the workers were arranging the dynamite and electrical cables on Wednesday, it rained and a lightning struck near the construction site, triggering the explosion. Local police were investigating the accident's cause.