GENEVA, Switzerland - A Patek Philippe gold watch billed as the most expensive in the world fetched a record $21.3 million (17.1 million euros) on Tuesday when it went under the hammer in Switzerland.

The sale of the "Henry Graves Supercomplication", a handcrafted timepiece named after its original owner, a New York banker who ordered it in 1925, was the main event at a jewel and watch auction held in Geneva.

The watch, which weighs more than half a kilo and comprises 900 separate parts, had been estimated to go for a lower amount, $15 million.

But frenzied bidding between five hopeful buyers pushed the price up ever higher over 15 minutes, and the final amount paid was "a new world record," Sotheby's said.

The winning bidder, who remained anonymous, will have to fork out a total of $24 million, including the commission.

It took Patek Philippe five years to put the watch together. Graves's name is right there on the dial.

It was the most complicated watch built for 56 years, and is only superseded in that regard by later watches built with computerised assistance.

Tim Bourne, Sotheby's worldwide head of watches, said the sale confirmed the watch's "superstar status".

Bourne called it an "icon of the 20th century, a masterpiece that elevates the discipline of watchmaking to art".

- 'Symbolises strength, power and money' -

A watch industry expert told AFP before the auction the timepiece was not just an immensely expensive accessory.

"This is not a watch you can wear. It is a watch that symbolises strength, power and money," he said.

The Patek Philippe piece displays not only the hour but also a plethora of other indicators: a perpetual calendar, the phases of the moon, sidereal time, indications for the time of sunset and sunrise, and the shifting night sky over Manhattan.

Its Westminster chimes sing joyfully every 15 minutes

The watch has been on the block once before, at a Sotheby's auction in New York in December 1999, when the Time Museum in Rockford, Illinois closed its doors and emptied its inventory.

That time, the exquisite timepiece went for a mere $11 million, again to a buyer who remained unidentified.

The watch was among 368 timepieces that were up for auction on Tuesday. The lots, including the Graves timepiece, fetched a total of $32.6 million.

- Jewels under the hammer -

Sotheby's and rival house Christie's were also both hosting their traditional Magnificent Jewel sales this week, with Christie's headlining its sale Tuesday with a piece drawn from the French Crown jewels.

The mythical diamond-decked "Feuilles de Groseillier" brooch was commissioned by Empress Eugenie in 1855 and was created by French jeweller Alfred Bapst.

Sotheby's was also presenting a bit of royal history at its competing auction on Wednesday, offering up a stunning pearl necklace that once belonged to Josephine de Beauharnais (1807-1876), who became queen of Sweden and Norway.

Sotheby's jewel chief David Bennet suggested the pearls, expected to fetch up to $1.5 million, may even have been handed down by the queen's grandmother and namesake, the first wife of Napoleon Bonaparte.

"It may well be that these pearls were originally in her collection as well," Bennet told AFP.

Sotheby's will also be offering several pieces from the Dimitri Mavrommatis collection of precious stones and avant-garde jewellery, led by the "Graff Ruby".

The glimmering 8.62-carat blood-red rock, mounted on a ring, was acquired by Graff in 2006 for $3.6 million and later sold to Dimitri Mavrommatis for an undisclosed sum.

It is expected to fetch $6.8-9.0 million at Wednesday's auction.

Wealthy collectors from around the world have descended on the Swiss city for the action-packed days at the two competing auction houses.