The coins were discovered Monday as a landowner was moving soil on his property, The Local.se reported.
"This is an amazing find. It's unbelievable that treasures of this scale exist here on Gotland," Marie Louise Hellquist of Gotland's County Administrative Board said.
Some 500 coins were found by the landowner and about 150 more were found after archaeologists arrived on Wednesday.
Jewellery and a raw silver artifact, believed to be part of an ancient axe, have also been found at the site.
Hellquist said some of the coins date to the year 1130.
Experts will examine the findings to determine what the treasure may be worth, Hellquist said, adding that she hopes the items will stay on the island in a museum.