The Ham Tan District traffic police said the people were from the central Quang Tri, Ha Tinh and Nghe An provinces, and were trying to return home surreptitiously from Ho Chi Minh City, where they had been living.

They had been told to gather outside a supermarket in Dong Nai's Bien Hoa Town that borders HCMC on Sunday, and picked up in two cars.

At Long Khanh Station in Dong Nai, they were transferred to the truck, which had permission to pass through Covid checkpoints on National Highway 1.

At around 10 p.m., on reaching Binh Thuan, the truck stopped near a restaurant two kilometers away from a checkpoint in Tan Duc Commune.

Traffic police officers patrolling the highway became suspicious and ordered the driver Le Van Tuan, 39, to open the doors, and found 14 adults and a seven-year-old boy inside.

"The truck had not turned on its refrigeration," a police officer at the scene said.

Tuan said the two cars had been rented.

The 15 passengers, who all had negative coronavirus test certificates, claimed they did not know they would be transported in a refrigerated truck.

They have been quarantined in Ham Tan District, and an investigation is ongoing.