A hire company has said it is “shellshocked” and “gutted” after 39 Chinese people were found dead in one of its trailers.

A spokesman for Global Trailer Rentals Ltd (GTR) confirmed it owned the part of the lorry which was found on an industrial estate in Grays, Essex, on Wednesday containing the bodies of the eight women and 31 men.

The refrigerated trailer was leased on October 15 from Global Trailer Rentals’ yard in Co Monaghan, in the Republic of Ireland, at a rate of 275 euro (£237) per week, the spokesman told RTE News on Thursday.

The company said it provided police with information about the person and company that leased the trailer, as well as offering to make tracking data available.

Its directors said the company was “entirely unaware” the trailer was to be used in this manner.

READ MORE: Essex lorry deaths: 39 found dead 'were Chinese nationals'

Detectives have been given an extra 24 hours to question the driver.

A 25-year-old man, named locally as Mo Robinson, from Northern Ireland was arrested on suspicion of murder and remains in custody.

Officers are to start the process of removing the bodies from the lorry – which has been moved to nearby Tilbury Docks – and take them to a mortuary so post-mortem examinations can begin.

The bodies are expected to be taken in a private ambulance under police escort in several convoys to Broomfield Hospital in Chelmsford by the weekend.

Deputy Chief Constable Pippa Mills said the post-mortem and identification process will be “lengthy and complex”.

Bodies found in lorry containerDeputy Chief Constable Pippa Mills speaks to the media (Victoria Jones/PA)

The discovery echoes one in 2000 when the bodies of 58 Chinese illegal immigrants who had paid a criminal gang to be smuggled into the UK were found in a sealed, airless container in Dover.

Home Secretary Priti Patel met with officers from the force on Thursday morning.

Meanwhile, local dignitaries and police gathered to open a book of condolence.

Thurrock councillor James Halden said the discovery was “devastating” and it was a “very dark day” for the town.

READ MORE: Opinion matrix; Divided views on how to end the people smugglers' death toll

The trailer arrived at Purfleet from Zeebrugge in Belgium at around 12.30am on Wednesday, and the front section to which it was attached, known as the tractor, came from Northern Ireland via Holyhead in North Wales on Sunday.

The lorry and trailer left the port at Purfleet shortly after 1.05am and officers were called around 30 minutes later after ambulance staff made the discovery at Waterglade Industrial Park in Eastern Avenue.

Lorry container deaths: key locations(PA Graphics)

The deaths follow warnings from the National Crime Agency (NCA) and Border Force of the increased risk of people-smuggling via Belgium and into quieter ports such as Purfleet.

The NCA previously said it had a “greater focus” on rising smuggler numbers in Belgium after the closure of a migrant camp, and a Border Force assessment highlighted Zeebrugge as being among “key ports of embarkation for clandestine arrivals”.

The agency also warned criminal networks are suspected to have started targeting quieter ports on the east and south coasts of the UK as well as the main Channel crossing between Calais and Dover.

READ MORE: Essex lorry deaths: What we know so far as 39 bodies found in trailer

The day after the incident, a group of suspected migrants were seen being detained in Zeebrugge, with some of them seen trying to climb a fence into a compound attached to a truck company before they were intercepted by police.

Bodies found in lorry containerShipping containers at the port of Zeebrugge in Belgium – where the trailer travelled from to Purfleet (Gareth Fuller/PA)

Lorry drivers told of a “constant battle” to stop migrants trying to get into their vehicles.

But port bosses insisted such trailers are “completely sealed” in the port so it was unlikely people were loaded into the container there.

But they said the cargo may not have been checked as it passed through Belgium to the UK.

Three addresses in Northern Ireland were searched on Wednesday as part of the investigation.

Councillor Paul Berry said the village of Laurelvale, near Portadown, where the Robinson family live, was in “complete shock”.