Early indications are that 38 adults and one teenager have died, Essex Police said. The force said the lorry came from Bulgaria and entered the country via Holyhead on Saturday.
Early on Wednesday, at around 1.40 a.m. the ambulance service was called after the macabre discovery at Waterglade Industrial Park in Eastern Avenue, Grays.
Andrew Mariner, a senior officer said police were trying to identify victims but anticipated a "lengthy process", the BBC reported.