Three people have been treated for minor injuries after an unidentified substance was delivered to a restaurant in London's Borough Market.
Police were called to Feng Sushi, in Stoney Street, at 1.38pm on Thursday.
London Fire Brigade said firefighters using protective equipment were called to assist police with a "chemical incident" following the delivery of an envelope containing the substance.
The irritant was identified by police soon after as naturally occurring.
The incident is not being treated as terror-related "at this early stage", the Metropolitan Police has said.
London Ambulance Service treated three people at the scene for minor injuries, but none of them required hospital treatment. The property was evacuated as a precaution.
Local businessman Paul Dawson said he arrived at the restaurant just after the police.
"There were two uniformed police in there... the manager was flustered and said 'sorry, we've had something quite bad happen, we have to close'," he said.
No arrests have been made and police are continuing with their inquiries.