The 39 people found dead in the back of a truck in the UK were all believed to be Chinese nationals, authorities confirmed Thursday.

The dead — including a teenage girl — were found packed in the back of a Scania truck in Grays, Essex, at 1:40 a.m. Wednesday.

“We have since confirmed that eight of the deceased are women and 31 are men and all are believed to be Chinese nationals,” Essex police said in a statement, with one of the females a teenager.

“Each of the 39 people must undergo a full coroner’s process to establish a cause of death,” the force said, warning it was a lengthy and “substantial operation.”

The container they were packed inside appeared to be refrigerated, with temperatures as low as minus 13 degrees F, according to Road Haulage Association chief exec Richard Burnett, who said it would have been “absolutely horrendous” inside.

Authorities were quick to blame human traffickers — with specialist officers looking at potential “organized crime groups who have played a role,” the National Crime Agency confirmed on Twitter.

Driver Mo Robinson, 25, was still being held on suspicion of murder Thursday as officers raided three other properties in Northern Ireland.

His dad learned of his son’s arrest through social media, according to local councilor Paul Berry, who said the village of Laurelvale in County Armagh was in “complete shock,” according to the BBC.

“The local community is hoping that he [Mo Robinson] has been caught up innocently in this matter but that’s in the hands of Essex Police, and we will leave it in their professional hands to try to catch the perpetrators of this,” he said.

The truck was registered in Bulgaria to a company owned by an unidentified Irish woman, the Bulgarian Foreign Ministry said.