The jewels are encrusted with gold, pearls and precious stones and are from the 1611 funeral regalia of Sweden's Charles IX and Kristina the Elder.
Eyewitnesses told the Aftonbladet that two men were spotted fleeing from the cathedral. Royal Central reports that the crowns were burial crowns that were later exhumed and put on display at the cathedral.
"It's 1-0 to them right now", police spokesperson Thomas Agnevik said.
The thieves, who have not been identified, and the jewels are being sought internationally via Interpol, Swedish police spokesman Stefan Dangardt said, noting the objects were a "national treasure" and would likely be "very hard to sell".
The motorboat is described as small and open, though its color is now unclear.
'The girls said it was odd, in this small quiet town but the fact that the boat was waiting, it was obvious to me that they were burglars. "We have spoken to witnesses, but we are interested in further information from anyone that has made any observations", he said.
They asked the public for help, while Sweden's main news agency, TT, said an global inquiry for the artifacts would be made in Interpol's system.
Police sent out a helicopter and boat to hunt for the thieves but found nothing.
Thieves have made off with priceless Swedish crown jewels, in a daring heist reminiscent of a Hollywood movie.
Maria Ellior, an official with the Swedish police's National Operations Department, told the local TT news agency Wednesday that the items would be "impossible to sell".
"It's despicable that people would steal from a holy building", he said.
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