Fifteen people have been arrested on suspicion of immigration offences after being discovered in the back of a lorry in Wiltshire. In addition, a man in his 50s from Ireland has been arrested on suspicion of assisting with illegal entry into the country.

Wiltshire police said they closed the A350 at the Kington Langley crossroads near Chippenham on Wednesday after being called by a member of the public shortly before 8.30pm.

Officers attended the scene and 15 people – all believed to be males aged between 16 and 30 – were found in the back of the vehicle. Ambulance service staff carried out initial medical checks on the group, and all but one were deemed fit and well and were taken into custody.

One person was taken to the Great Western hospital in Swindon as a precaution but was later released into custody. Wiltshire police said the force was “not clear” about the nationalities of the 15 at this stage.

Supt Steve Cox said the road was closed for about four hours while emergency services worked at the scene and arrangements were made to remove the lorry, a hard-sided large goods vehicle.

“I fully understand that recent tragic events elsewhere in the country will mean there will be increased interest and heightened concern regarding this incident,” he said on Thursday.

“I’d like to thank all emergency services who responded last night. As with all incidents, we didn’t know the scale of what we would potentially be dealing with, and all first responders showed true professionalism at the scene.

“I would also like to extend my thanks to the vigilant member of the public who initially reported this incident to us. It is thanks to them that this incident was resolved swiftly and safely, with no serious casualties.”

The incident follows the arrest of eight people earlier this week by Vietnamese police in connection with the 39 migrants found dead in a lorry in Essex. They were held on Sunday on suspicion of organising people smuggling overseas.

The 31 men and eight women who were discovered in the back of the refrigerated truck in Grays in October are thought to have been Vietnamese. So far two people have been charged.

Essex police have started extradition proceedings to bring 22-year-old Eamonn Harrison from Ireland to the UK.

Harrison, from Newry, Northern Ireland, appeared at Dublin high court last Friday charged with 39 counts of manslaughter, along with human trafficking and immigration offences, and was remanded in custody.

The driver of the lorry, Mo Robinson, 25, appeared at Chelmsford magistrates court charged with 39 counts of manslaughter, conspiracy to traffic people, conspiracy to assist unlawful immigration and money laundering.

Detectives have also urged Ronan Hughes, 40, and his brother Christopher, 34, who are said to have links with the road haulage and shipping industries, to hand themselves in. The pair, from Armagh, Northern Ireland, are wanted on suspicion of manslaughter and human trafficking.