LONDON — The 39 people found dead inside a truck at an industrial estate near London are believed to be Chinese, police said Thursday as more details emerged.

“Each of the 39 people must undergo a full coroner’s process to establish a cause of death before we move on to attempting to identify each individual within the trailer,” police said in a statement.

Officials added that 31 are men and eight are women, and all are thought to be adults. Police earlier said a teenager was among the dead.

Chinese officials swiftly reacted to the latest announcement.

“We read with heavy heart the reports about the death of 39 people in Essex, England,” China’s Embassy in London said in a statement to NBC News.

The story has also been a popular topic on Chinese social media with posts on the deaths on Weibo reportedly read 400 million times.

Police also raided three properties in Northern Ireland after the bodies were found in a container on the site in Grays, about 20 miles east of central London in the early hours of Wednesday. They arrested the driver, a 25-year-old man from Northern Ireland, on suspicion of murder.

The trailer had arrived at the docks in Essex, southern England, having traveled from Zeebrugge in Belgium, and the bodies were found just more than an hour later at 1:40 a.m., officials said.

The red cab unit of the truck was believed to have originated in Ireland. It had “Ireland” emblazoned on the windscreen along with the message, “The Ultimate Dream.”

Prime Minister Boris Johnson said he was appalled by the news and was receiving regular updates about the investigation, which was focused on human trafficking.

The National Crime Agency — which leads probes into organized crime and human trafficking — said it was assisting the investigation and working to “urgently identify and take action against any organized crime groups who have played a role in causing these deaths.”

Nick Bailey and F. Brinley Bruton reported from London, Dawn Liu reported from Beijing.