British police say they have arrested two more people on suspicion of human trafficking and manslaughter over the deaths of 39 people found in a truck in Essex.

Key points: Three arrests have now been made in relation to the bodies found in a truck in Essex

Three arrests have now been made in relation to the bodies found in a truck in Essex Chinese Foreign Ministry calls for greater "cooperation, sharing of information and early intervention" of human trafficking

Chinese Foreign Ministry calls for greater "cooperation, sharing of information and early intervention" of human trafficking China is still seeking confirmation of the identity and nationalities of the deceased

A man and a woman, both aged 38, were arrested in Warrington, northern England, Essex police said.

The driver of the truck, a 25-year-old man from Northern Ireland, remains in police custody having been arrested on suspicion of murder.

The arrests come as police prepare to begin post-mortem examinations on the bodies.

"The first 11 victims are being transported under police escort by private ambulance from the Port of Tilbury to Broomfield Hospital in Chelmsford having left the port at 7:41pm (on Thursday)," police said in a statement.

"The process of victim recovery under the Disaster Victim Identification (DVI) process is likely to take some time.

"The next stages will be for post-mortem examinations to be carried out."

The victims, all believed to be Chinese nationals, would have been inside the trailer they were found dead in for at least 12 hours, Belgian authorities said.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 3 minutes 49 seconds 3 m 49 s The deadly routes and risks involved in people smuggling in Europe

Joachim Coens, chief executive of Zeebrugge port in Belgium, said the trailer was sealed and the dock was monitored by cameras, meaning it was likely the 31 men and eight women climbed into the container before it reached the port.

Mr Coens said the trailer would not have been touched after it arrived at Zeebrugge at 2:49pm on Tuesday (Belgium time).

The container was then shipped unaccompanied to the United Kingdom, where emergency services were alerted to the discovery at the Waterglade Industrial Park in Grays, Essex, almost 12 hours later at 1:40am the next day (UK time).

"A refrigerated container in the port zone is completely sealed," he told Belgian media.

"During the check, the seal is examined, as is the licence plate. The driver is checked by cameras."

Dirk de Fauw, the mayor of Bruges, told Belgian public broadcaster VRT there was extensive camera coverage at Zeebrugge up until the loading of the ferry.

"[To] break the seal, bring 39 people onboard and apply a new seal without being noticed, that chance is extremely small," he said.

China calls for crack down on human trafficking

It comes after China called for joint efforts to counter human smuggling after the discovery of the bodies west of London, all of whom are believed to be Chinese migrants.

Authorities say those on board were likely on the truck for 12 hours before discovery. ( AP: Stefan Rousseau )

Foreign ministry spokeswoman Hua Chunying told reporters at a daily briefing that China could not yet confirm the victims' nationalities or identities but was working in cooperation with local authorities.

"The British police are still in the intensive process of verification and are still unable to confirm at the moment," Ms Hua said.

"But I think that no matter where these victims come from, this is a great tragedy which drew the attention of the international community to the issue of illegal immigration.

"I think the international community should further strengthen cooperation in this area, strengthen sharing of information and intelligence in this regard, and conduct early intervention in these activities so as to prevent such tragedies from happening again in the future."

Ms Hua said Chinese authorities were also seeking information from police in Belgium, from where the shipping container in which the bodies were found was transported to England.

Human smuggling from China is believed to have fallen drastically in recent years amid a rapidly growing domestic economy.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 38 seconds 38 s The UK Police detailed the lengthy process to identify the 39 victims in Essex.

However some Chinese, particularly those with lower education levels, continue to be drawn to Europe and North America by the promise of much higher wages than they can earn at home, despite the considerable risks involved.

Parts of China, especially the south-eastern province of Fujian, have long histories of sending migrants abroad.

The issue is a difficult one to confront for China's ruling Communist Party, which is intensely sensitive about China's international image and has staked much of its legitimacy to rule on improving living standards for the bulk of China's 1.4 billion people.

In an editorial Friday, the party newspaper Global Times said authorities in Britain and elsewhere hadn't done enough to crack down on people smuggling.

"Such a serious humanitarian disaster occurred under the eyes of the British and Europeans," the newspaper said.

"Britain and the related European countries have not met their responsibility for protecting these people from dying in such a manner."

ABC/Wires