Police are trying to work out how thieves managed to steal paintings by Van Gogh, Picasso and Gauguin, worth an estimated £1m from a city centre gallery.
Van Gogh painted The Fortification of Paris with Houses
Staff at Whitworth Art Gallery in Manchester uncovered the theft as they prepared to reopen at about 1200 BST on Sunday.
The masterpieces - Van Gogh's The Fortification of Paris with Houses, Picasso's Poverty and Gauguin's Tahitian Landscape - could have been stolen at any time after 2100 BST on Saturday.
Greater Manchester Police have described the raid as "well planned".
They spent Sunday combing the gallery for evidence. Officers said several other items had also been taken.
The gallery, on Oxford Road, south of the city centre, has been closed to the public.
Picasso created Poverty in 1903
Its collection of 40,000 works of art is designated as of
national significance by the government.
It includes 12 Picassos and Van Gogh's Hayricks, as well as sculptures, drawings, prints, wallpapers, historic textiles, British watercolours, and modern and contemporary art.
Dutchman Vincent Van Gogh painted The Fortification of Paris with Houses in 1878, at the age of 25, using pencil,
chalk and watercolours.
Between 1891 and 1893, Parisian Paul Gauguin, who was born in 1848, created his dramatic Tahitian Landscape with pencils and watercolours.
And in 1903, a 24-year-old Pablo Picasso, of Malaga, Spain, used pen, ink and blue watercolours to create Poverty, the
outline of a frail man guiding a small child.
The largest of the three masterpieces measures 39 by 53 centimetres (1ft 2in by 1 ft 9in), a police spokesman said.
Andrew Graham-Dixon, a writer and presenter of the BBC television series Renaissance, said the raid could have been carried out by "naive thieves" hoping to re-sell the paintings.
If that was the case, he warned the publication of the robbery by officers leading the inquiry could prompt those behind the theft to burn the evidence.
The gallery, which has been part of the University of Manchester since 1958, regularly changes exhibits
and gives access to reserve collections.
Gauguin used pencils and watercolours on Tahitian Landscape
Founded at Grove House in 1889, it is named after Sir Joseph Whitworth, a
Stockport-born engineer who left it money.
The first displays included plaster casts and Morris & Co tapestries Flora and Pomona.
Anybody with any information about the theft or who may have been in the
Whitworth Park area on Saturday evening is urged to contact police on 0161 856 4450.