A man in New Orleans called the police on Friday after suspects allegedly posing as art removal experts attempted to steal a mural by the graffiti artist Bansky.
By the time the call was made the two suspects had gone, leaving the mural intact.
The artwork, locally known as Umbrella Girl or Rain Girl, depicts a mournful girl holding an umbrella from which rain pours on to her as she extends a cupped hand into the open air around her.
Photographer Cheryl Gerber noticed plywood had been erected around the painting on her way home from work on Friday.
She asked a man sitting at the back of a nearby rental truck what was going on, to which he replied: “Oh, the picture is going to London for a big show”.
She returned home and posted a photo showing a wide gap above the painting which was hidden behind a plywood screen, on Facebook.
Her message read: “Bye Bye Banksy! My neighbourhood's most famous little girl is moving to London”.
Clay Lapeyrouse, the operations manager at Louisiana Fresh Produce, was alarmed when he saw the post.
When he asked the suspects to show him their permits for working on the building, they could not provide any but told him the building's owners wanted to send the painting to a museum.
“They couldn't tell me who the owner was or the name of the museum,“ Mr Lapeyrouse said, adding: “I called the police and called every authority I could think of in the city.”
Mr Lapeyrouse said he stayed to guard the mural for as long as he could, but finally left to get his dogs from day care.
When he returned the men had gone, but he stayed in case they came back. More neighbours arrived and Mr Lapeyrouse said he also tore down the plywood screen.
John Guarnieri, office manager at an architectural firm and a board member of the Bywater Neighbourhood Association, said eventually a former tenant of the building arrived and was able to give the name of the owner's lawyer.
Police spokesman Officer Garry Flot said an investigation into the incident has begun but the identities of the suspects remain unknown.
A guard is now protecting the painting and a new plywood shield has been put up, neighbours said.
New Orleans resident Charlie Varley, who grew up south of London, also saw the man chopping at the wall.
Mr Varley said the man told him he was a Los Angeles ”art handler“ working for the building owners, who were sending it to the Tate Modern - one of four Tate museums holding Britain's national art collection.
Banksy, whose works have sold at auction for as much as £660,000, created the mural after Hurricane Katrina in 2005.
It is among a dozen made in 2008 in the US state of New Orleans by the mysterious artists, many of which have been painted over or destroyed.
Tate spokeswoman Jeanette Ward said there ”are currently no plans announced to include the work of Banksy in an exhibition“.
Additional reporting by AP