The Big Maple Leaf, worth £2.7mn, was stolen from a Berlin museum last night
Thieves broke in to the Bode Museum in Germany's capital in the early hours of the morning and made off with the 100 kilogram "Big Maple Leaf" coin.
The Canadian coin, measuring 53cm in diameter and 3cm thick, is made out of pure gold and bears the image of Queen Elizabeth II on one side and a maple leaf on the other.
Its face value is CA$1m but its material value is estimated to be about four and a half times higher, making it worth CA$4.5 (£3.5m).
The museum's website said the coin was issued by the Royal Canadian Mint in 2007 and it was featured in the Guinness Book of Records for its "unmatched" degree of purity.
It was loaned to the Bode Museum in December 2010.
The coin weighs 100kg
Police said the coin was probably stolen by a group of thieves who entered the museum undetected through a window at about 3.30am on Monday, possibly with the help of a ladder they stole from nearby railway tracks.
A spokesman from the museum said the thieves entered through the window before breaking into a cabinet where the "Big Maple Leaf" was kept, and they escaped with it before police arrived.
Berlin Police spokesman Winfried Wenzel, said: "Based on the information we have so far we believe that the thief, maybe thieves, broke open a window in the back of the museum next to the railway tracks.
"They then managed to enter the building and went to the coin exhibition.
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The coin has a maple leaf on one side and the Queen on the other side
The coin was stolen Berlin's Bode Museum, which had loaned it from the Royal Canadian Mint
"The coin was secured with bullet-proof glass inside the building. That much I can say.
"Neither I nor the Bode Museum can go into detail regarding personnel inside the building, the alarm system or security installations."
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The Bode Museum, based on the UNESCO-listed Museum Island, has one of the world's largest coin collections with more than 540,000 items .