Hooded raiders have stolen a van containing some 20 pieces of art reportedly including a Picasso drawing.
Other works included pieces by Colombian artist Fernando Botero and Spanish sculptor Eduardo Chillida.
The van was taken from a warehouse near the town of Getafe on Madrid’s southern outskirts.
Police refused to say exactly what was stolen but the Spanish newspaper El Mundo and other media said it included a Picasso drawing, and paintings, engravings and sculptures from some of the other artists.
The daily ABC said the art was valued at least five million euro (£4.2 million).