At least one of the 39 people found dead in a refrigerated lorry container near London might have originally come from Vietnam, a Vietnamese human rights activist said on Friday citing relatives of a woman who paid smugglers to get into the UK. Pham Thi Tra My, 26, sent a text message to her mother saying she was suffocating at about the time on Tuesday that the lorry container was travelling via ferry from Belgium to the UK. "It was told on the news that all 39 people were Chinese but Tra My's family is trying to verify if their daughter was among them as the last dying text from her was co-incidently intime," Vietnam-based activist Hoa Nghiem wrote on Twitter. "Our contact is getting more alerts that there could be more Vietnamese people in the truck." The BBC reported that Ms Tra My's family paid £30,000 (Dh141,000) for her to be smuggled to the UK. The broadcaster said it had been in contact with the families of a 26-year-old man and a 19-year-old woman also from Vietnam, who feared their relatives could be among the dead. Three more people have been arrested in connection with the deaths, police announced on Friday. A man and a woman, both 38, from Warrington, northern England and a 48-year-old man from Northern Ireland, who was stopped at Stansted Airport in Essex, have been arrested on suspicion of manslaughter and conspiracy to traffic people. The driver of the lorry is still being questioned by UK police as post-mortem examinations began on some of the victims. The bodies of 11 of the victims – 31 men and eight women originally believed to be Chinese nationals – were moved to a hospital mortuary on Friday morning. Police said the nationality of the dead was a "developing picture". The arrests come after China said authorities in the UK should seek “severe punishment” for those involved. The 25-year-old driver from Northern Ireland, who has been named by sources close to the investigation as Mo Robinson, was arrested on suspicion of murder after the discovery at Grays, Essex, 30 kilometres east of London. "This is the largest investigation of its kind Essex Police has ever had to conduct and it is likely to take some considerable time to come to a conclusion," Essex Chief Constable Ben-Julian Harrington said. Police are determining the identity of the dead, how they died and who was involved, in what experts suspect, was a human trafficking ring. China said police had not yet been able to verify the nationalities of the deceased. "We hope that the British side can as soon as possible confirm and verify the identities of the victims, ascertain what happened and severely punish criminals involved in the case," Foreign Ministry spokeswoman Hua Chunying said in a news briefing. The Chinese Embassy in the UK said it had sent a team to Grays. Police said they were focusing on determining the movement of container prior to its arrival at Purfleet docks, near Grays, on Wednesday from Zeebrugge, Belgium. The chairman of Zeebrugge port, Dirk de Fauw. said he believed the victims had died in the container before it arrived at the Belgian port. The container is believed to have arrived at 2.39pm local time in Zeebrugge on Tuesday, according to The Times newspaper citing GPS data on the container’s movements. Detectives are trying to establish where the container had travelled from. The lorry cab entered the UK on Sunday from Dublin at the Welsh port of Holyhead. The lorry picked up the container from Purfleet at around midnight on Wednesday, little more than an hour before the bodies were found. The deaths bring back tragic memories from 2000 when 58 Chinese migrants suffocated in a truck in Dover, England, after a month’s-long journey from China. China’s Global Times, published by the ruling Communist Party's official People's Daily, said the UK had not learned its lesson from the Dover tragedy nearly 20 years ago. "It is clear that Britain and relevant European countries have not fulfilled their responsibility to protect these people from such a death," the widely-read tabloid said. Grace Forrest, co-director and founder of the Walk Free Foundation and UN Association of Australia goodwill ambassador for anti-slavery, said despite the UK’s efforts to combat trafficking, people smuggling operations continue to operate under the radar of the police. "No country is immune to human trafficking… vulnerable people are taking more extreme and risky measures in trying to get work and it puts them in the hands of people who run organised crime syndicates, people smugglers," she told <em>The National</em> in an interview at the One Young World conference in London. “There is increasing vulnerability of human trafficking, of organ trafficking, forced labour and many other forms of extreme exploitation and if you're not seen within a system it cannot protect you.” The Walk Free Foundation estimates that more than 130,000 people are victims of modern-day slavery in the UK, many of whom have come to the country via human trafficking. Slavery is the most profitable organised crime in the world, amounting to a $150 billion global industry.