The majority of the 39 people found dead in the back of a truck near London were likely from Vietnam, a community leader from the rural, rice-growing community where many of the victims are believed to have come from told Reuters on Saturday.
The discovery of the bodies - 38 adults and one teenager - was made on Wednesday after emergency services were alerted to people in a truck container on an industrial site in Grays, about 32km (20 miles) east of central London.
Police have said they believe the dead were Chinese but Beijing said the nationalities had not yet been confirmed. Chinese and Vietnamese officials are now both working closely with British police, their respective embassies have said.
Father Anthony Dang Huu Nam, a catholic priest in the remote town of Yen Thanh in northern-central Vietnam's Nghe An province, 300km (180 miles) south of Hanoi, said he was liaising with family members of the victims.
"The whole district is covered in sorrow," Nam said, as prayers for the dead rang out over loudspeakers throughout the misty, rain-soaked town on Saturday.
"I'm still collecting contact details for all the victim's families, and will hold a ceremony to pray for them tonight."
"This is a catastrophe for our community."
Nam said families told him they knew relatives were travelling to the UK at the time and had been unable to contact their loved ones.
Vietnam's foreign ministry said in a statement on Saturday that it had instructed its London embassy to assist British police with the identification of victims.
The ministry did not respond to a request for further comment regarding the nationalities of the dead.
Nghe An is one of Vietnam's poorest provinces, and home to many victims of human trafficking who end up in Europe, according to a March report by the Pacific Links Foundation, a U.S.-based anti-trafficking organisation.
Other victims are believed to come from the neighbouring province of Ha Tinh, Nam said, where in the first eight months of this year, 41,790 people left looking for work elsewhere, including overseas, according to state media.
The province was ravaged by one of Vietnam's worst environmental disasters in 2016 when a steel mill owned by Taiwan's Formosa Plastics contaminated coastal waters, devastating local fishing and tourism industries and sparking widespread protests.
One suspected victim from Ha Tinh, 26-year-old Pham Thi Tra My, had sent a text message to her mother saying she could not breathe at about the time the truck container was en route from Belgium to Britain.
"That girl who said in her message that she couldn't breathe in the truck? Her parents can't breathe here at home," Nam said.