British police have found the bodies of 39 people inside a lorry believed to have come from Bulgaria at an industrial estate to the east of London and said they had arrested the driver on suspicion of murder.

The discovery was made in the early hours of Wednesday after emergency services were alerted to people in the truck container on a gritty industrial site in Grays, about 32 kilometres (20 miles) from central London.

The lorry is said to have originally started its journey in Bulgaria was thought to have entered the United Kingdom at Holyhead, a North Wales port that is a major entry point for traffic from Ireland, on Saturday, police said.

All those in the container, 38 adults and one teenager, were pronounced dead at the scene after the emergency services were called to the Waterglade Industrial Park, not far from docks on the River Thames.

Bulgaria’s foreign ministry said it could not confirm at this stage whether the truck had started its journey from the country.

“We are still checking the information, published in the British media and we’re contacting the authorities,” foreign ministry spokeswoman Tsvetana Krasteva said.

In Britain’s biggest undocumented immigrant tragedy in 2000, British customs officials had found the bodies of 58 Chinese people crammed into a tomato truck at the southern port of Dover.