Armed robbers have stolen the iconic Edvard Munch painting, The Scream, from the Munch Museum in Norway.
The robbers fled with the painting to a waiting car
Two masked thieves pulled the work and another painting, Madonna, off the wall as stunned visitors watched on Sunday.
One robber threatened staff with a gun before the pair escaped in a waiting car, a museum officer told the BBC.
The car was later recovered and police also found parts of picture frames near to where a witness reported seeing a suspect vehicle.
The Munch Museum said the two stolen paintings were among its most valuable - worth an estimated $19m (£10.4m) together, according to the BBC's Lars Bevanger.
Norwegian Culture Minister Valgerd Svarstad Haugland described the theft as "dreadful and shocking".
HOW THE SCREAM WAS STOLEN
1. Two masked men enter through the museum cafe
2. One man holds staff and visitors at gunpoint
3. The other man goes to the gallery and tears the Scream and Madonna from the walls
4. The two men make their escape, fleeing in a black Audi
"We have not protected our cultural treasures adequately. We must learn the lessons," she said.
Jorunn Christofferson, a press officer at the Munch Museum, told the BBC the museum was full of people when the robbers took the two paintings - frames and all - off the walls of the gallery.
Kjell Pedersen of the Oslo police told the Norwegian daily Aftenposten that police had "mobilised all available resources on the ground and in the air".
Nobody was hurt and no shots were fired, Ms Christofferson said.
She said the museum had closed-circuit television that would have captured the event on video, but that the thieves "were wearing black hoods, like bank robbers".
A French radio producer who was in the museum at the time of the theft said security was not very tight.
"What's strange is that in this museum, there weren't any means of protection for the paintings, no alarm bell," Francois Castang told France Inter radio, the Associated Press reported.
"The paintings were simply attached by wire to the walls," he said. "All you had to do is pull on the painting hard for the cord to break loose - which is what I saw one of the thieves doing."
Ms Christofferson said the guards were more concerned with protecting visitors than the paintings.
"When they threaten the guards with a gun there is not much to be done," she told the BBC.
"They were more concerned with the security of the visitors."
Munch painted several versions of his famous 1893 work.
Another version of the painting - considered to be the most significant one - was stolen from the Norwegian National Gallery in 1994 as the Winter Olympic Games began in Lillehammer, Norway.
The Norwegian government received a demand for a ransom of $1m, but never got proof that those demanding the money had the painting.
An anti-abortion group claimed it could get the painting returned if an anti-abortion film was broadcast on television.
Police dismissed that claim.
The painting was recovered undamaged in a hotel about 65km (40 miles) south of Oslo in May 1994. Three Norwegians were arrested in connection with the theft.
Munch, Norway's best-known artist, died in 1944, aged 81.