Two paintings with a combined value of £82,000 are missing, believed stolen, from Somerset House in central London.
The paintings have been on display at Somerset House since 2006
The paintings, on display at the Navy Board Rooms since 2006, were reported missing last Wednesday, the Department for Culture, Media and Sport said.
One was a 1764 portrait of Sir William Chambers, the building's architect, by English artist Francis Cotes.
The other was Shipping, by artist John Thomas Serres, dating back to 1821. Police have launched an investigation.
A part of Somerset House has been home to various offices of the Navy Board for about a century.
A statement from the Department for Culture, Media and Sport said: "The pictures were installed in Somerset House in February 2006.
"This was at the request of the Somerset House Trust for display in the refurbished Portico Room Suite (South Wing of Somerset House) which the trust uses for public, educational and corporate events."