It later emerged they had been caught after rare antiquities dating back to the era when Yin Xu was a royal capital were found on sale just a stone’s throw away from the archaeological site.

Police said the site and only been partially excavated by archaeologists and some parts had remained untouched for millennia.

“It is hard to determine the severity of these thefts from the recovered objects alone,” one unnamed officer told Henan news website Dahe.cn.

“The key issue is that they damaged the layers of soil at the archaeological site, which could cause further loss or destruction.”

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Many of the artefacts stolen were bronze drinking vessels and engravings, police said.

Anyang police received a tip-off last August when a member of the public warned that antiques that appeared to have been stolen were on sale in the village of Xiaozhuangcun on the outskirts of the modern city of Anyang – just a stone’s throw from the historic site.

Although few details of their investigation have been made public they found that the tomb raiders had been operating from a rented house and a local restaurant from where they burrowed into the ancient royal burial sites, Henan Daily reported on Monday.

The L-shaped hotel tunnel, the entrance to which was only wide enough for one person to pass through at a time, had started in the basement of the building and was around three metres deep and 10 metres long, Dahe.cn reported.

Police found excavation tools, numerous bags of soil and ventilation machines at the crime scene.

It is not known exactly how long the raids have been going on for, but police believe the thefts date back to at least 2013.

The main suspects were detained in the surrounding area last August and September. These included a villager who rented out the house and the party secretary of nearby Sipanmocun village, identified only by his surname Wang, who is suspected of being the leader of one of the criminal gangs involved in the thefts.

People who were suspected of buying and selling the stolen items across a number of Chinese provinces were also detained.

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Police have not disclosed the total value of the haul they recovered but they said individual items had been sold for the equivalent of hundreds, if not thousands, of dollars.

Anyang police released what appeared to be a confession by one member of the crime syndicate in which he said he had realised there were probably valuable items in the tombs when he learned that the Cultural Relics Department was carrying out inspection work at the site.

Police said they have since stepped up security at the tombs.

Yin Xu, some 500 kilometres (310 miles) south of Beijing, was the last capital city of the Shang dynasty, which ruled between approximately 1600BC and 1050BC.

It is the first Chinese dynasty for which archaeological evidence exists, including bronze objects that are celebrated for their quality and craftsmanship.

The 30 sq km archaeological site includes a number of palaces and burial grounds where elaborate burial offerings such as chariots and bronze ceramics have been unearthed as well as oracle scripts carved on bones, the earliest form of Chinese writing.