The paintings disappeared early Thursday from the Paris Museum of Modern Art, across the Seine River from the Eiffel Tower. Investigators have cordoned off the museum, in one of the French capital's most tourist-frequented neighborhoods.
The museum's security system was disabled, and a single masked intruder was caught on a video surveillance camera, according to Christophe Girard, deputy culture secretary at Paris City Hall.
Investigators are trying to determine whether the intruder was operating alone, Girard told reporters. He said three guards were on duty overnight but "they saw nothing."
The intruder entered by cutting a padlock on a gate and breaking a museum window, the Paris prosecutor's office said.
The prosecutor's office initially estimated the five paintings' total worth at as much as euro500 million ($613 million).
Girard, however, said the total value was "just under 100 million euros."
He said "Le pigeon aux petits-pois" (The Pigeon with the Peas) an ochre and brown Cubist oil painting by Pablo Picasso, was worth an estimated euro23 million, and "La Pastorale" (Pastoral), an oil painting of nudes on a hillside by Henri Matisse about euro15 million.
The other paintings stolen were "L'olivier pres de l'Estaque" (Olive Tree near Estaque) by Georges Braque; "La femme a l'eventail" (Woman with a Fan) by Amedeo Modigliani; and "Nature-mort aux chandeliers" (Still Life with Chandeliers) by Fernand Leger.
Alice Farren-Bradley of the Art Loss Registry in London said the Paris theft "appears to be one of the biggest" art heists ever, considering the estimated value, the prominence of the artists and the high profile of the museum.
She added, however, that the value of the paintings would have to be confirmed, as museums and art dealers often value paintings differently.
Interpol did not immediately respond to calls seeking comment on the theft or its possible role in the investigation. The police organization has coordinated international searches for stolen masterpieces in the past.
Red-and-white tape surrounded the museum, where investigators were studying surveillance video. Paper signs on the museum doors said it was closed for technical reasons.
On a cordoned-off balcony behind the museum, police in blue gloves and face masks examined the broken window and empty frames. The paintings appeared to have been carefully removed from the disassembled frames, not sliced out.
A security guard at the museum said the paintings were discovered missing by a night watchman just before 7 a.m. (0500 GMT, 1 a.m. Thursday EDT). The guard was not authorized to be publicly named because of the museum policy.
Paris Mayor Bertrand Delanoe said in a statement that he was "saddened and shocked by this theft, which is an intolerable attack on Paris' universal cultural heritage."
The director of the neighboring modern art museum Palais de Tokyo, Pierre Cornette de Saint-Cyr, called the thief or thieves "fools."
"You cannot do anything with these paintings. All countries in the world are aware, and no collector is stupid enough to buy a painting that, one, he can't show to other collectors, and two, risks sending him to prison," he said on LCI television.
"In general, you find these paintings," he said. "These five paintings are un-sellable, so thieves, sirs, you are imbeciles, now return them."