Three of Sweden's crown jewels, dating back to the 17th century, were stolen Tuesday in a brazen daylight heist.

Two crowns and an orb are missing, and the thieves still at large. They fled from the church first by bicycle and then by motorboat, and an international search is underway.

The golden, jewel-encrusted crowns and orb were on display at the Strängnäs Cathedral, west of Stockholm, near the banks of Lake Malar.

"The objects, which are of high historical and economic value, were stored according to prevailing safety regulations in locked and armed displays which at the time of the theft were open to visitors," the Church of Sweden said in a statement.

But in the middle of the day on Tuesday, burglars smashed the glass, setting off alarms, and stole the two crowns and the orb, a cathedral spokeswoman told The Associated Press.

There was no violence involved, and no threat of violence, the church said in its statement.

"Several people then left ... in a boat just below the church," Swedish police said in a statement.

Police say the thieves "are suspected of leaving the church on bicycles" — and two black bicycles, possibly stolen, were found near the shores of the lake near where the boat disappeared.

Police tried to locate the culprits, including with a search by helicopter, to no avail.

Now divers are hunting for clues in the lake, The Associated Press reports. (Are authorities perhaps concerned that the getaway boat was a red herring and the real extraction was carried out underwater, a la the remake of The Italian Job? Alas, the wire service doesn't specify.)

The search is complicated — Lake Malar is crowded with islands and ringed by towns and cities. By boat, thieves could have reached anywhere from Stockholm in the east to Arboga in the west, some 80 miles apart, a police spokesman told local media.

"Police said the thieves could have fled further on jet skis, adding it was only a theory," the AP reports.

The missing artifacts will be registered with Interpol, and authorities say the stolen items are so recognizable they'd be difficult, if not impossible, to sell, The Local reports:

" 'Images are being shown in the media. It's simply not possible to sell these kind of items. So you can only wonder what their intentions are, and how much they know about these crowns,' Maria Ellior from the Swedish Police National Operations Department (Noa) told news agency TT."Registering the theft with Interpol means 'even international police will be on their toes,' she added, noting that the theft was likely well planned."

In 2013, a 16th-century Swedish royal scepter and crown were stolen from the Västerås Cathedral and then recovered in a pair of trash bags on the side of a highway, the local news service notes.

NPR's Liana Simstrom contributed to this report.

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