A British court on Thursday heard harrowing accounts from the families of 39 Vietnamese migrants who were found dead in the back of a lorry, as the smugglers responsible await sentencing.

Haulier boss Ronan Hughes, one of the gang's ringleaders, closed his eyes at London's Old Bailey court as he heard recordings of the victims' distressing final moments.

In one message, a man struggled for air as he apologised to his family, saying "I can't breathe.

"I want to come back to my family. Have a good life," he added, as distressed noises from other victims were heard in the background.

The dead men and women were found by lorry driver Maurice Robinson inside a sealed container near London in October 2019.

Hughes, Robinson, fellow lorry driver Eamonn Harrison and Romanian gang boss Gheorghe Nica were all convicted on 39 counts of manslaughter at a trial which ended last month.

They face potential life sentences. Sentencing is due on Monday. Another four people convicted of involvement are also set to find out their fate.

The victims' families spelled out the human and financial cost of the tragedy in statements read out by prosecutor Jonathan Polnay in court.

Nguyen Huy Tung, whose 15-year-old son Nguyen Huy Hung died in the tragedy, said the family "did not believe it was the truth until we saw his body by our own eyes" at the hospital.

"We were very shocked, trembled, we lost track and awareness of our surroundings," he added. "My wife had fainted many times whenever our son's name was mentioned."

Bui Thi Nguyet, who lost her son Dinh Dinh Binh, also 15, said: "Although we have received his cremated ashes and organised his funeral, we have not been able to get back to our normal life yet.

"Our economic conditions and work are negatively affected. We have had to sell some properties of the family to afford our life."

Tran Hai Loc and his wife Nguyen Thi Van, both 35, left behind two children, aged six and four, when they perished on the journey.

"Everyday, when they come home from school they always look at the photos of their parents on the altar," said the children's grandfather Tran Dinh Thanh.

"The (death) of both parents is a big loss to them."

The migrants' bodies were discovered at the southeastern English port of Purfleet after being sealed inside the container for at least 12 hours, in unbearably high temperatures.

A forensic expert calculated it would have taken about nine hours for the air to turn toxic in the trailer, with death coming soon after.

The victims were all aged between 15 and 44.

Prosecutors have said the trapped Vietnamese migrants were unable to get a phone signal inside the container, whose cooling system was turned off.

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