(CNN) Thieves stole priceless royal artifacts in a daring raid on a Swedish cathedral before escaping by speedboat, police said.

The thieves made off with jewels belonging to former Swedish monarchs Karl IX and Kristina from the Strängnäs Cathedral to the west of the capital, Stockholm, on Tuesday.

Two crowns and a golden orb adorned with a crucifix were taken from the cathedral, which dates back to the 12th century, according to a police report. The items date from the early 17th century.

A witness told Swedish media that he was eating lunch when he saw two people running toward a boat, which they sped away in.

Police said several thieves were involved in the heist. They fled in an open-topped motorboat across the sea from the base of the church. Several police patrol boats as well as police helicopters joined a hunt for the perpetrators.

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