Over 32 pieces of jewellery including gold and pearls, dating 1,500 years, have been found on the island in Horsens Fjord, according to broadcaster DR.
The gold included beads, pendants, a needle and small gold pieces that were used as currency during the Iron Age.
The first pieces of the treasure were uncovered by amateur archaeologist Terese Refsgaard, a dental assistant from Aarhus, in spring 2017.
“Years can go by without amateur archaeologists finding gold, and some never do, so this is amazing,” Refsgaard told DR.
Mads Ravn, head of research at Vejle Museums, said the gold was thought to date from just before the Viking period and was likely buried around 500 CE.
The find suggests that people from Hjarnø had contact with the Roman empire, Ravn said.
“They probably took part in raids there, so our find is a small legacy from a turbulent time in world history in which gold speaks its own clear language,” Ravn told DR.
The pieces will now be analysed in order to further clarify their origin.
Some of the jewellery has patterns and designs not previously seen, the head of research said.
“In terms of craft, they are completely unique, with gold markings that almost form spirals,” he said.
“That is evidence of a high level of skill,” he added.
The treasures will be displayed at Vejle’s Museum of Cultural History before later being sent to the National Museum of Denmark in Copenhagen.