Swedish police were said to be chasing them by boat, helicopter and in cars. The monarchs were initially buried with these crowns, but later exhumed, NBC News said.
"The two men hurriedly jumped on board".
They asked the public for help, while Sweden's main news agency, TT, said an worldwide inquiry for the artifacts would be made in Interpol's system.
A picture taken on July 31, 2018 shows a cordoned zone as Swedish police investigate after Sweden's royal jewels dated from the 17th century were stolen from the Strängnäs cathedral, west of Stockholm.
The crowns and orb are made of gold and enamel and encrusted with beads, crystals and pearls.
Thieves snatched some of Sweden's crown jewels before escaping in a speedboat as part of a Hollywood-style heist in broad daylight.
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"We are on land, in the water and in the air", a police spokesperson told the Sydney Morning Herald.
The witness claims he knew something was up because of the way "they were behaving".
The motorboat is described as small and open, though its color is now unclear.
Police said in a statement that they were alerted to the theft at 11.44am. "We have some different information about how exactly the boat looked", Thomas explained.
Tom Rowsell, who was having lunch outside the cathedral where he is to be married this weekend, told Swedish newspaper Aftonbladet he saw two men dash from the building toward a motorboat waiting on Lake Malaren.
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".