The four stolen paintings are: "Poppies near Vetheuil" by Claude Monet (1879), "Count Lepic and his Daughters" by Edgar Degas (1871), "Chestnut in Bloom" by Vincent Van Gogh (1890) and "Boy in a Red Jacket" by Paul Cezanne (1888), police said.
Lukas Gloor, the museum's director, said that the stolen paintings were "the four finest in the museum's collection".
He also said that they were well known and therefore impossible to sell on the open market.
Sarah Jackson, a representative from the Art Loss Register, which maintains a database of stolen and missing art, told Al Jazeera: "These were really priceless pictures and... quite impossible to sell on the legitimate art market.
|"These were really priceless pictures |
and... quite impossible to sell on the legitimate art market"
Art Loss Register
"It is possible that the thieves... will try to recover a reward put out for their safe return. Or they may be passed between gangs as some form of bargaining chip."
Police said that one of the robbers used a pistol to force museum personnel to the floor while the two others went into the exhibition hall and collected the four paintings.
They loaded the paintings into a white van parked in front of the museum.
A reward of about $90,000 has been offered for information leading to the recovery of the paintings.
The Emil Buehrle Foundation is a private collection founded by a Zurich industrialist and includes many pieces of Impressionist and post-Impressionist art.
It holds more than 200 paintings, including seven Van Goghs and Cezannes, six Degas and five by Monet.
The theft comes just days after two paintings by Pablo Picasso worth $4.5m were stolen from a cultural centre in eastern Switzerland.