The Louvre has been forced to close after staff walked out in protest at what is said to be a rising problem of pickpockets haunting the Paris museum's vast galleries.
A spokeswoman was unable to say when the museum, which normally attracts up to 30,000 visitors a day at this time of year, would reopen.
Crowds of disappointed tourists gathered outside. "We've been cheated," said US student Mariam Kamel, 16.
Her teacher, Rhonda Eastman, said she had given specific instructions to her students to avoid being pickpocketed while in Paris.
"On the metro they no longer speak English, they don't stand together, they're snobs," she said.
Louvre officials could not provide an exact figure for the number of pickpocketing victims, but the museum said that it was a growing problem despite measures taken last year including tighter cooperation with the police. The Louvre said it would crack down on repeat offenders through temporary bans on entry into the museum.
The Louvre claims to be the world's most visited museum, with nearly 10 million visitors last year.