An 800-year-old "made in China" label has helped archaeologists pinpoint when an ancient merchant ship sunk.

After a fisherman discovered a lost treasure-trove of ancient ceramics off the coast of Indonesia in the 1980s, archaeologists have struggled to piece together where the ship was from and when it sunk, as the wooden ship disintegrated long before its contents were discovered.

They initially dated the ship to the 13th century, however new evidence suggests it is "probably a century older than that", according to Lisa Niziolek, an archaeologist at the Field Museum in Chicago and lead author of the study in the Journal of Archaeological Science: Reports.

Among the thousands of ceramics found in the shipwreck, some were marked with an inscription that suggests they were made in Jianning Fu, a government district in China near modern-day Jian'ou.

This is a significant find as the district was reclassified as Jianning Lu after the Mongols invaded around 1278.

From this find Ms Niziolek and her colleagues were able to deduce that the shipwreck might have occurred earlier than 1200, possibly as early as 1162.

There were probably about 100,000 pieces of ceramics on board. It seems unlikely a merchant would have paid to store those for long prior to shipment — they were probably made not long before the ship sank, said Ms Niziolek.

Elephant tusks and incense resins found in the cargo have also helped date the shipwreck. Carbon dating on the items carried out when they were found in the 1990s revealed them to be about 700-750 years old.

However the scientific techniques used to date carbon atoms found in once-living specimens have since improved, allowing scientists to reveal that the tusks and resins are closer to 800 years old.

Ms Niziolek said: "When we got the results back and learned that the resin and tusk samples were older than previously thought, we were excited.

"We had suspected that based on inscriptions on the ceramics and conversations with colleagues in China and Japan, and it was great to have all these different types of data coming together to support it."

The fact that the shipwreck is 800 rather than 700 years old is significant as it occurred during a time of "important transition".

Ms Niziolek explained: "This was a time when Chinese merchants became more active in maritime trade, more reliant upon over-sea routes than on the overland Silk Road."