Six stowaways were caught on a Finnish ro-ro in the UK after calling emergency services in desperation.
The Sun reported that the African men had boarded owner Bore's 25,600-gt Bore Song (built 2011) in Zeebrugge, Belgium, last month.
When it reached Teesport in England, they dialled 999 and said: "We are stuck in a container."
The migrants had become desperate by 2 April after being locked in the container for more than a day following its arrival in the UK at the end of March.