“This item has gone beyond the scope of existing knowledge,” he told the state news agency Xinhua.

The cage “is unique in shape, exquisite in craftsmanship and ingenious in design. It can be imagined that people cherished it at the time,” Li added.

The team also found some gold pieces at the back of the jade when cleaning the cage, which could be opened as soon as Thursday.

But the archeologists were even more intrigued by the jade stone inside, and hope it might provide important clues to the ancient civilisation that produced it.

‘Unprecedented’: 13,000 artefacts from mysterious Chinese kingdom found

Since the start of mass excavation in the 1980s, the huge number of artefacts unearthed at the site suggest the presence of a realm that had reached a high level of economic prosperity and technological advancement.

In some large pits for religious sacrifice, archaeologists have found some of the largest and most sophisticated bronze wares in the ancient world, including a “tree of life” nearly four metres (13 feet) tall, face masks made of gold, and bronze “sheets” as thin as printing paper.

But the Shu kingdom that is believed to have occupied the area left no written records behind, leaving researchers guessing at the beliefs and practices behind the discoveries.

Lei Yu, curator of the Sanxingdui Museum, said the team hoped to find some scripts or writings on the jade stone.

Before removing the cage from the pit, researchers detected the presence of some fabric, probably silk, over the surface of the jade and bronze ridges, he said.

The silk may have some writings on it and Lei said he hoped there would be carved characters on the jade itself.

“We can only use instruments to detect some traces. The information will exist in fragments,” he told the state broadcaster CCTV. “But I believe there is a written language there.”

Some Sanxingdui bronze wares previously found carried some patterns on their surface that appeared to be symbols, but none have been identified as a language.

Thousands of jade artefacts, many of which are thought to have come from a prehistoric quarry in the mountains about 40km (25 miles) from the site, have been found at Sanxingdui before.

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Archaeologists find treasures from mystery civilisation that could rewrite Chinese history

Archaeologists find treasures from mystery civilisation that could rewrite Chinese history

But this is the first time a jade has been found locked in an expensive cage like this anywhere in China, and Li said there must have been an important reason for doing so.

“It might have something to do with the spiritual world,” he said in an interview with state television.

Li’s team called the cage “Pandora’s Box” – although the name comes from the celebrated 1990s Hong Kong movie, A Chinese Odyssey Part 1 – Pandora’s Box, in which the box serves as a portal for time travel rather than unleashing untold evils on the world as in the Greek myth.

Researchers say newly found sites in China date back as far as 3,200 years

In the latest round of excavations, archaeologists found some items suggesting a culture exchange between the two civilisations.

A bronze sculpture, for instance, featured a man carrying over his head a vessel commonly found in the Yellow River sites that formed the Shang’s heartland.

However, some researchers believe the Shu are more likely to have maintained stronger connections with societies in Southeast Asia or India.