As many as 1,000 homes are being evacuated after a suspected unexploded Second World War device was found at a school.
A 300-metre exclusion zone has been set up following the discovery at Lansdown Road in Bath where contractors using a digger unearthed the device at Royal High School.
Those living nearby are being evacuated to Bath Racecourse and motorists are being asked to find alternative routes as some roads in the area are closed.
Inspector Gavin Usher of Avon and Somerset Police said: "We would like to thank everyone who has been inconvenienced for their patience while we deal with this incident.
"Decisions to evacuate houses are never taken lightly but during these incidents public safety will always be our primary concern."
The "large" device was discovered at around 4.40pm as excavation work was carried out at the the site and the Explosive Ordnance Disposal team was alerted, Force Incident Manager Inspector Rob Pearson said.
At around 6pm, after studying pictures of the find, police were instructed to set up a cordon and evacuate those properties within it.
Asked how long the incident may last, Pearson said: "We anticipate that it is not going to be resolved this evening."
He said a range of emergency services were involved in a "multi-agency approach to keep people safe".