Burglars took period pocket watches with a retail value of around £200,000 when they broke into the Vintage Watch Store at the Hampstead Antique Emporium on Saturday, April 11, at about 9.40pm.
In a further burglary attempt on the premises at 10.45pm on Sunday, April 12, the thieves were disturbed by a neighbour and left without gaining entry.
Simon Drachman of the Vintage Watch Store said: "They entered through a disused air-conditioning shaft, which allowed access after clambering over the roof of the building and removing the fan cover and fan unit itself.
"The robber or accomplices had clearly made a careful study of the security cameras' positions and how to enter and leave the building, carefully knocking cameras, so no images could be seen if they were the swivelling type.
"The watches taken were all pocket watches (except for two gents' Omega wristwatches).
"They consisted of key-wind gold or silver examples including many with rare escapements such as Sully or Massey 4, or watches by famous makers like Thomas Earnshaw and Robert Roskell.
A rare 18k gold Royal presentation watch from King Oscar II of Sweden from c.1910 of about 5in diameter was also taken.
"All the major pocket watch dealers in the UK have been alerted and a full list with links to our website has been sent out," said Mr Drachman.
The watches can be seen among other items at http://stores.ebay.co.uk/TheVintageWatchStore
Anyone with any information should contact Det Con Adele Joyner on 020 8733 6913 or call Crimestoppers anonymously on 0800 555 111.