Berlin police say thieves broke into the German capital's Bode Museum and made off with a massive 100-kilogram gold coin issued by the Royal Canadian Mint that's worth millions.

Dubbed the "Big Maple Leaf" and measuring three-centimetres thick with a diameter of 53 centimetres, the coin has a portrait of the Queen on one side and maple leaves on the other.

It has a face value of $1 million, but by weight alone it would be worth approximately $4 million US at market prices.

The museum, which has one of the largest coin collections in the world, said on its website that the coin has been on loan in its numismatic collection since 2010.

It was first issued by the Royal Canadian Mint in May 2007 and was listed in the Guinness Book of Records for its purity: 99.999 per cent gold. 

Spokesman Stefen Petersen said thieves apparently entered through a window at about 3:30 a.m. local time on Monday, broke into a cabinet where the coin was kept, and escaped with it before police arrived.

A ladder was found by nearby railway tracks.

Royal Canadian Mint spokesman Alex Reeves said the stolen coin does not belong to the mint. After creating the original (which is in storage in Ottawa), the mint manufactured five more that were sold to interested private individuals. 

The owner of the stolen coin is unknown.