The thieves hid in the Schirn public gallery shortly before closing time, then bound and gagged the guard and escaped with the paintings using the service lift.
Shade and Darkness - the Evening of the Deluge, and its companion Light and Colour (Goethe's Theory) - the Morning After the Deluge - Moses Writing the Book of Genesis are among the most important of Turner's late work and form part of the Turner bequest. They are valued at over pounds 10m each and are insured with Lloyd's of London.
Nicholas Serota, director of the Tate Gallery, said: 'These are two of the most important works in the Turner Bequest and masterpieces of European Romanticism. Their theft represents a major loss for the Tate Gallery and for European painting.'
The German gallery, host to major international exhibitions, admitted yesterday that its special night-time alarm system had not yet been switched on. The thieves - police said there were at least two of them - also took a painting by the leading German romanticist, Caspar David Friedrich. The value of the three paintings was put at pounds 28m.
First exhibited in 1843, Shade And Darkness and Light And Colour are examples of Turner's late style at its most highly developed. In them Turner expresses the biblical story of The Deluge in contrasted colour schemes. The paintings form a pair, and are exhibited together. They measure 78.5cm by 78cm each, and were stolen with their frames.
Sabine Schulze, in charge of the temporary exhibition Goethe and Art at the Schirn gallery, said: 'The theft must have been carried out by organised criminals, or be politically motivated. The paintings are just too valuable.'
'These priceless works are totally unsellable,' said Hellmut Seemann, director of the Schirn gallery. He speculated that the thieves might seek to return the masterpieces to the insurance company in exchange for money.
Mrs Schulze said the Tate Gallery and the Hamburg Kunsthalle, which had loaned the Friedrich, had allowed the exhibition to continue without the stolen works. 'They have been very understanding,' she said. 'A theft like this is the worst thing that could happen to a gallery. It is an absolute nightmare.'
The Turners were due to return to the Tate after the close of the exhibition on 7 August.
A spokeswoman for the Tate said that the Tate and other British national collections had lent works to the Schirn Kunsthalle before without incident. It is fitted with modern alarm systems and has been approved by the National Security Adviser for loans from British galleries.
(Photograph omitted)Reuse content