The Sikhs, discovered at Tilbury Docks in Essex, east of London, feared they would have all died had they remained inside for any longer without food or water, Kamaljit Singh Mataharu, a Punjabi-speaking local man called in by the police to translate, told reporters.
"It was pitch black, without any air. It soon became extremely uncomfortable," he told ITV television.
"Horrendous, horrendous, horrendous. They suffered a lot," he said.
It has emerged that there were 15 families inside the container, all from Kabul, who had made it to Europe in a truck.
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"They were in a bad state. According to a little boy they'd been in the container for roughly 18 hours," said Mataharu.
The container had arrived on a truck at Zeebrugge 12 hours before the people inside were discovered at Tilbury.
"They'd been banging on the container... They'd tried for hours and hours for somebody to hear their voices. They are thanking God they are alive. Another 20 minutes... All would've been dead in there," the translator said.
The illegal immigrants from Afghanistan were found screaming and banging for help inside the container on Saturday.
The officer leading a homicide inquiry after the man's body was found inside along with 34 other people said members of the Sikh community from Tilbury were assisting officers and helping to care for the stowaways.
They were hospitalised and those released from hospital include nine men and eight women and 13 children. Four survivors still remain in Southend hospital.
A post-mortem examination was carried out on the body of the deceased yetserday but further tests are set to be undertaken to establish the cause of death.