The 39 people found dead in the back of a lorry in Essex were Chinese nationals, sources said. 

Officers in Northern Ireland have raided two houses and the National Crime Agency said it was working to identify "organised crime groups who may have played a part".

READ MORE: Essex lorry deaths: 'They dreamed of a new and better life...'

Ambulance staff discovered the bodies of the eight women and 31 men in the container at Waterglade Industrial Park in Grays yesterday. 

Originally, Essex police reported that the lorry had travelled into the country through Holyhead on Saturday.

Officers have set up a casualty bureau for anyone to call if they have concerns about relatives who may be involved.

Police are continuing to question a 25-year-old man from Northern Ireland on suspicion of murder.

In a statement Essex Police said there were eight women and 31 men among the 39 people found dead in a lorry trailer in Grays, Essex, on Wednesday.

The force, which said the case is the largest murder investigation in its history, said officers believe they are all Chinese nationals.

A statement said: “Of these, 38 are believed to be adults, and one is a young adult woman. We previously reported that she may have been a teenager. We have since confirmed that eight of the deceased are women and 31 are men and all are believed to be Chinese nationals. We arrested a man on suspicion of murder, who remains in custody.

READ MORE: Fears for more migrant tragedies after 39 bodies found 'frozen to death' in container 

“We want to be clear – we have not speculated about the identity of this man, and we will not do so. We can confirm that three properties in County Armagh have been searched in connection with our investigation.

“The lorry has since been removed from the industrial park to allow the next stage of our investigative process to be conducted in peace, and to give the utmost dignity to those within the trailer as we prepare for a coroner’s post-mortem examination.

“Each of the 39 people must undergo a full coroner’s process to establish a cause of death, before we move on to attempting to identify each individual within the trailer. This will be a substantial operation and, at this stage, we cannot estimate how long these procedures will take.”