More Vietnamese families have come forward with information that their relatives may be among the 39 people found dead in the back of a container truck in Essex.

Police are continuing to question four people in connection with the tragedy.

Police had initially said they believed the victims were Chinese but have acknowledged that this is a “developing picture” and the nationality of the victims have not been confirmed.

In a statement on Saturday, the Vietnamese ministry of foreign affairs said it had asked the Vietnamese embassy in London to collaborate with police and help identify victims.

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, told Reuters he was liaising with family members of the victims.

“The whole district is covered in sorrow,” Nam said, as prayers rang out over loudspeakers in the 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 Britain at the time the container truck would have been travelling and had been unable to contact their loved ones.

A representative for VietHome, which serves Vietnamese people in the UK, said it had sent the pictures of nearly 20 people reported missing to the police.

News of the lorry deaths has dominated social media in Vietnam. Families of those with missing children have also been calling out for help on Facebook.

Relatives of Nguyen Dinh Luong, 20, shared in a post on Facebook that they fear he may be one of the victims, while numerous other families have called out for help. The family of Vo Nhan Du, 19, posted on Facebook to ask for help finding him. Du reportedly left for the UK on the same day as Luong and Pham Thi Tra My.

On Friday fears were raised that 26-year-old Pham may have been on the lorry after text messages emerged from Pham to her mother saying: “I’m dying because I can’t breathe.” Her family have heard nothing from her since.

Despite photos of Pham circulating online, police are yet to confirm if she is among the dead. Pham had travelled to China before going on to Europe, and reportedly paid £30,000 to reach the UK.

Her texts were shared by Hoa Nghiem, the coordinator at Vietnam-based NGO Human Rights Space, who was concerned about Pham’s whereabouts following contact from the girl’s family. Hoa, among others, now fears many other Vietnamese people may have been in the truck.

“My local contact confirmed five other families from the same district submitted a report to the police about their family members,” Hoa said.

Other Vietnamese people in the UK have shared their knowledge about the number of missing people and the identity of those in the lorry.

In a Facebook post shared at 1.38am GMT, Pham Van Nho, a PhD student at United World Colleges’ London campus who is working with police in London to identify victims in the lorry, claimed the number of Vietnamese people in the lorry may be far higher.

“I now have information of 21 family members and acquaintances of people who have gone ‘missing’,” he said, before adding that he would not reveal more details to the press without further information from police.

It is being reported in Vietnamese media that authorities are pressing charges against a woman from Yen Thanh district, in Nghe An province, for human trafficking.

Nghe An, the province where many of the potential victims are from, is one of the poorest in Vietnam and a hotspot for human trafficking, according to the human trafficking NGO Blue Dragon Children’s Foundation, an organisation that rescues victims of human trafficking from China.

Michael Brosowski, the organisation’s chief executive, said when he “first heard that there were 39 people who died in a truck on the way to the UK. Honestly my first thought was that this was news about Vietnam.”

He added: “I do know that traffickers and smugglers use every available route to get people from Vietnam to the UK and it seems in this case that this girl and possibly others may have come from Vietnam into China, possibly legally.

“Most likely in this case, there are multiple trafficking rings in multiple countries, each of whom will be taking a cut from this trade. I heard she paid £30,000. That money will be divided among many people. These people are professionals.”

An Nguyen, 23, a university student in Hanoi, said: “It’s such a tragedy. The parents just innocently hope for their children to have a better life. There’s no future living in the poor province of Ha Tinh.”

Hundreds of Vietnamese people are trafficked to the UK each year according to the UK-based charity Ecpat. Often, they are forced to work in slavery in nail bars or cannabis farms.

In 2000, 58 Chinese migrants died from asphyxiation in a refrigerated truck in Dover.