The 39 suspected migrants found dead in a trailer shipped from Belgium to Britain all believed to be Chinese nationals, British police said, report agencies.
We have since confirmed that eight of the deceased are women and 31 are men and all are believed to be Chinese nationals, police said in a statement on Thursday.
China's foreign ministry said it was trying to confirm the reports that people found dead in the back of a truck near London were Chinese, the Global Times reported in a tweet on Wednesday.
The paper, published by the official People's Daily newspaper of China's ruling Communist Party, said the foreign ministry told the newspaper nothing could be released as of now.
Belgian prosecutors confirmed the container was shipped from the port of Zeebrugge on Tuesday.
Essex Police were questioning a 25-year-old man from Northern Ireland who was arrested on suspicion of murder after the bodies were found early on Wednesday, adding that raids had been carried out at three properties in Northern Ireland.
Police Service Northern Ireland searched the properties in the Northern Irish village of Laurelvale, County Armagh late Wednesday, where the driver and his family lived, the Belfast Telegraph reported.
The vehicle has been moved to a secure site at nearby Tilbury Docks where the bodies can be recovered and further forensic work undertaken to begin what police said would be the lengthy process of identifying the victims.
The National Crime Agency said it was assisting the investigation and working to urgently identify and take action against any organised crime groups who have played a role in causing these deaths.
Shaun Sawyer, the national spokesman for British police on human trafficking, said many thousands of people were seeking to come to the United Kingdom. While they were able to rescue many of those smuggled into the country, Britain was perceived by organised crime as a potentially easy target for traffickers.
You can't turn the United Kingdom into a fortress. We have to accept that we have permeable borders, he told BBC radio.
For years, undocumented migrants have attempted to reach Britain stowed away in the back of trucks, often seeking to reach the United Kingdom from the European mainland.
In Britain's biggest illegal immigrant tragedy, the bodies of 58 Chinese people were found crammed into a tomato truck at the southern port of Dover in 2000. The vehicle had begun its journey in Zeebrugge.