The truck in which the migrants were found was being used to transport timber (Picture: AFP)

Four people have been arrested after the bodies of 18 dead migrants were found in Bulgaria.

The bodies, including one of a child, were discovered in an abandoned truck outside the village of Lokorsko, a short distance from the capital city of Sofia. 

Borislav Sarafov, head of the country’s National Investigative Service, said they had likely suffocated. 

The migrants are believed to have crossed the Turkish border before hiding in the forest for two days. 

Sarafov said they were then likely loaded into the vehicle near to the southeastern city of Yambol, and concealed in compartments within the truck, which was also transporting timber.

Authorities say 34 migrants, including five children, were found alive and rushed to hospitals, where they remain in critical but stable conditions. 

Health Minister Asen Medzhidiev said: ‘There has been a lack of oxygen to those who were locked in this truck. They were freezing, wet, they had not eaten for several days.’

Police confirmed that one of the four people arrested following the gruesome discovery had already been sentenced on charges of human trafficking. 

The abandoned truck, outside the village of Lokorsko, Bulgaria, where on Friday police discovered the bodies of 18 deceased migrants (Picture: AFP)

A total of 52 people had been hidden under wooden planks. Those who survived were rushed to hospitals in Sofia, about 20km southwest, where they are understood to remain in critical but stable condition (Picture: AFP)

Officials believe the deceased most likely died as a result of suffocation (Picture: AFP)

Most of those discovered in the truck are believed to have made the journey from Afghanistan. Bulgaria sits on a primary route used by migrants from the Middle East and further afield attempting to reach wealthier Western European countries (Picture: AFP)

Authorities added that more charges would follow once further evidence had been processed. 

Earlier in January, Europol announced the arrests of more than 92 human smugglers in Bulgaria. 

The country sits on a key route used by migrants, mostly from the Middle East and Afghanistan, as an alternative to making the deadly Mediterranean crossing between Turkey and Greece. 

Most of those making the perilous journey are seeking to enter the European Union, choosing not to stay in ‘transit countries’ like Bulgaria and preferring instead to move on to wealthier Western European states. 

Back in December, the EU blocked Bulgaria’s bid to enter the Schengen Zone, largely due to security concerns raised by Austria and the Netherlands. 

It is understood Bulgaria will make a further attempt to join the passport-free travel arrangement sometime this year. 

Such cases recall an incident in October 2019, at a shipping yard in Essex, when police discovered the bodies of 39 Vietnamese migrants who’d suffocated in the back of a container, sparking one of the largest homicide investigations in British history.