The accident took place at 11:55am as the monks were walking along a road near the entrance to Huai Sing area at Na Si Nuan village, reports the Bangkok Post.
According to local reports, the monks were travelling from Nam Khun district in Ubon Ratchathani province and had reached the area near the Na Si Nuan Market in Mukdahan when the crash took place.
Five monks died at the scene, while three others later succumbed to their injuries at Mukdahan Hospital. Eighteen monks were injured, 13 seriously.
However, investigations are continuing and the exact number of deaths and injuries could change.
Before the tragedy, the group of 34 monks had taken a meal at Wat Roi Phra Phutthabat Phu Manorom and then resumed their pilgrimage on foot towards Don Tan district in Mukdahan.
Police said the vehicle involved was an Isuzu pickup truck driven by a boy, aged around 11 years old. The child, described as having special needs, reportedly took his father’s vehicle without permission and drove from Don Tan towards Muang district.
The pickup reportedly veered into the group of monks, striking a large number of them and causing multiple casualties.
The boy was taken to the Muang district police station for questioning.