Three people have been injured after an envelope containing an “unidentified substance” was delivered to an address in Borough Market, police say.
The property on Stoney Street - which photos on social media suggest is a restaurant - was evacuated “as a precaution” after police, paramedics and the fire service were called just after 1.30pm.
Three people were treated for minor injuries following the delivery.
The incident is not being treated as a terror-related incident, police said.
Photos on social media from the scene show emergency service workers crowded around Feng Sushi restaurant, while members of the public look on.
American tourist John Brent told the Sun Online that he was getting lunch with his family when they “saw the emergency services pull up all of a sudden”.
“A group of firefighters got out carrying loads of water and were rushing it into the sushi restaurant,” the 44-year-old said.
“I couldn’t see what had happened in there and thought there was a fire at first but someone told me it was a chemical attack.”
No arrests have currently been made in connection with the incident.
Borough Market was targeted by terrorists during the London Bridge attack in June, which saw three extremists crash into people in a car before stabbing pedestrians.
A spokesperson from the Met Police said: “Police were called at 13:38hrs on Thursday, 10 August to reports of an unidentified substance being delivered in an envelope to a business in Stoney Street, SE1.
“A crime scene is in place. No arrests have been made.”
Police enquiries into the incident are underway.