A nationwide hunt was underway Monday in Norway for armed thieves who barged into a lightly guarded Oslo museum in broad daylight and ripped the Edvard Munch masterpiece The Scream from the wall.

Experts said the paintings were worth tens of millions of dollars and the thieves will likely demand a ransom for their return.

Police are looking for three suspects after seeing a photo taken by a witness that showed Sunday's robbery in progress.

The picture appears to show three robbers, two of whom are walking to a black car with the paintings in hand. The third robber appears to be opening the trunk.

Later on Sunday, police found the robbers' getaway car, a black Audi A6. Inside they found fragments of the paintings' frames.

The brazen theft has ignited a debate on Norway's lax museum security, with critics demanding tighter measures. This is the third time since 1988 that Munch works have been stolen from a Norwegian museum, and the second time, after 1994, that a version of The Scream has been stolen.

Police finally recovered the work after three months in May 1994 and arrested three Norwegians who had reportedly demanded $1 million US in ransom.

Munch, a pioneer of the early 20th century Expressionist movement, made several versions of his key works, including The Scream, known for its anguished subject screaming under a lurid sunset sky.

Munch painted four versions of The Scream, all part of a series called "The Frieze of Life." The original is in Oslo's National Gallery, while the stolen work – the main reproduction – and another version were given to the Munch Museum after the artist's death. A private collector owns the fourth.

Two American tourists, Mary Vassiliou and daughter Christina, were next to one of the masked men when he tore down a painting on Sunday, the Norwegian newspaper Dagbladet reported Monday.

"We had just looked at the picture when we heard some noise behind us. We turned and saw a hooded man with black clothes and black gloves who was trying to tear down the picture," Mary Vassiliou said.

"At first I thought it was a crazy man who was trying to destroy the picture," she added.