A 13-year-old boy and an amateur archaeologist have unearthed a "significant" treasure trove in Germany which may have belonged to the legendary Danish king Harald Bluetooth who brought Christianity to Denmark.

Rene Schoen and his student Luca Malaschnitschenko were looking for treasure using metal detectors in January on northern Ruegen island when they chanced upon what they initially thought was a worthless piece of aluminium.

But upon closer inspection, they realised that it was a shimmering piece of silver, German media reported.

A dig covering 400 square metres (4,300 square feet) that finally started over the weekend by the regional archaeology service has since uncovered a trove believed linked to the Danish king who reigned from around 958 to 986.

Braided necklaces, pearls, brooches, a Thor's hammer, rings and up to 600 chipped coins were found, including more than 100 that date back to Bluetooth's era.