The accident occurred on the Mukdahan–Don Tan Road near Ban Na Wiang Kae in Na Si Nuan subdistrict of Mueang district, where a group of 35 monks and five lay followers were walking as part of a pilgrimage.

Initial reports indicated that three monks died at the scene, while the remaining victims succumbed to their injuries later in hospital.

Following the crash, Pol Col Prayut Rueanthongkham, superintendent of Mueang Mukdahan Police Station, instructed Pol Maj Wanlop Phothiwang, an inquiry officer, to inspect the scene and coordinate rescue efforts, The Nation reported.

Police found several injured monks lying by the roadside. Nearby was the suspected vehicle — a bronze-gold Isuzu single-cab pickup truck bearing Mukdahan licence plate BT-1944. The front of the vehicle sustained extensive damage in the collision.

Police Major General Pairoj Thaiphutsa told the BBC that preliminary information suggested the driver was a child with special needs. However, he did not provide any further details.

The boy's grandmother, 72-year-old Thongyun Pikunsri, told authorities that her grandson had special needs and had taken the pickup truck from home earlier that morning.

She said she was unaware of where he intended to go and had alerted police in an attempt to have the vehicle intercepted before the crash, according to The Nation.

The boy was taken to Mueang Mukdahan Police Station, where authorities have launched an investigation into the incident.

Phra Sompong, one of the monks who survived the crash, recounted the horrifying moments leading up to the tragedy in an interview with the BBC.

"I was chanting the meditation mantra 'Buddho, Buddho' when I saw a boy driving a pickup truck approaching. Suddenly, the truck came at full speed and crashed into us," he said in a video shared online by local rescue workers.

"Luckily, another monk and I managed to jump out of the way just in time. The first nine monks in the line survived, but those behind them were struck and thrown into the air."