The giant coin, dubbed Big Maple leaf, was taken early on Monday morning from the Bode Museum in Berlin.
"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," said police spokesman Winfrid Wenzel.
"They then managed to enter the building and went to the coin exhibition…The coin was secured with bullet-proof glass inside the building. That much I can say," he added.
According to the museum, the gold coin was issued by the Royal Canadian Mint in 2007 and has been entered in the Guinness Book of Records for its “unmatched” level of purity of 999.99/1000 gold.
It has a diameter of 53 centimeters and is 3 centimeters thick, and was displayed in the museum since 2010 as part of the Münzkabinett collection -- Berlin's main coin archive, which includes over than 540,000 objects.
Wenzel noted that the thieves were either “hired to do it by someone who wanted to have the coin, but it’s more likely that it will be melted down.”