Around 200 homes have been evacuated and a major incident declared after police arrested two men on suspicion of explosives offences.
Police carried out a warrant in Vulcan Street, Derby, and arrested two Polish nationals - one in his 40s and another in his 50s. They remain in custody.
Officers said locals might have heard a controlled explosion earlier as the Army's explosive ordinance division deals with the situation.
The incident is not being treated as a terrorism-related, and there is said to be no wider risk to the community.
Police, the fire service and the ambulance service were still at the scene early this evening.
The evacuation area covers:
Shaftsbury Crescent - in its entirety
Vulcan Street - in its entirety
Reeves Road - in its entirety
Shaftesbury Crescent - in its entirety
Harrington Street - from Holcombe Street to Vulcan Street
Baseball Drive - to Colombo Street
Cambridge Street - at Reeves Road and Shaftesbury Crescent
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Police were going door to door, and anyone affected is asked to prepare to be away from home for 24 hours.
Anyone already away from their property is asked to contact Derbyshire Police via Facebook Messenger on the force's website, or by calling 101.
A rest centre has been set up at the Salvation Army centre on Osmaston Road.
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