Police have asked two other suspects, Ronan and Christopher Hughes, to turn themselves in.

Essex Police detective Daniel Stoten used a press conference in Northern Ireland on Friday to urge the two brothers to surrender to police.

They are being sought for questioning about possible links to the discovery of the bodies on October 23.

Police say they have already spoke to Ronan Hughes by telephone but want to talk to the two in person.

Authorities have not yet identified the victims or said where they came from, but many are thought to have come from Vietnam, where families have raised concerns about missing loved ones.

Meanwhile, police in Vietnam arrested two people and summoned others for questioning on Friday on suspicion of involvement in the 39 deaths.

After 10 Vietnamese families reported their relatives missing, fearing they were among the victims, Ha Tinh regional police launched a criminal investigation into suspected human trafficking, a statement posted on their website said.

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Two people have been arrested and others brought in for questioning, it said.

The investigation would also look at similar incidents that occurred over the last five years.

On October 26, Vietnamese Prime Minister Nguyen Xuan Phuc ordered an investigation into alleged human trafficking activities after British police said at least some of the truck dead may have come from the south-east Asian country.

AP, Reuters