A man has been arrested and more than 50 houses evacuated after "suspicious items" were found when police carried out a search warrant at an address in Derby.
Police, fire crews and the military were all at the scene in King Alfred Street, Normanton, on Sunday as the incident unfolded.
In a statement, Derbyshire Police said bomb disposal experts were on site and houses were being evacuated in the area after officers carried out a warrant at about 11.30am on Sunday.
On Sunday night it was not yet clear what the "suspicious items" were that sparked the incident.
A man has been arrested and remains in police custody, the force said.
Images taken by local newspaper Derbyshire Live showed emergency services at the scene, including fire crews, police officers and bomb disposal experts.
They also reported police officers knocking on doors of nearby houses in the area, which is reportedly a popular area with students.
A statement from Derbyshire Police said: "More than 50 houses have been evacuated in Derby after a number of suspicious items were found during a warrant in the city.
"Officers attended a house in King Alfred Street, Stockbrook, at around 11.30am. A man has been arrested and remains in police custody.
"The Explosive Ordnance Disposal team are on site and a number of houses are currently being evacuated in King Alfred Street, Monk Street and Wolfa Street.
"Residents are asked to stay away from the area and those evacuated will be contacted when it is safe to return to their homes."
In a later update, the force said the incident was likely to continue into the evening as officers worked with the Explosive Ordnance Disposal team.
It added: "The force is liaising with Derby City Council to help those who require temporary accommodation while they are currently unable to access their homes.
"Residents who have been evacuated will be contacted once it is safe to return."
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