The world-famous British Museum was evacuated on Saturday after visitors reported eye irritation from what they thought was a chemical leak, officials said.
Police were called after some visitors reported a strange smell and stinging eyes, a police spokesman said.
A museum spokeswoman said the sprawling galleries were cleared after a supposed chemical incident was reported.
She said about 8,000 visitors would typically have been in the museum, whose collections include priceless and ancient objects from around the world, on a Saturday afternoon.
The fire brigade was also called but could not find the source of the smell and eventually gave the museum, a top London tourist attraction, the all-clear.
No-one required treatment. The museum was evacuated as a precaution. It has since reopened, the police spokesman said.
(Reporting by Adrian Croft; Editing by Jon Hemming)