A 20-year-old man has been arrested following an explosion which led to people being evacuated from their homes.
Officers believe the blast took place in Pound Bank Road in the Worcestershire spa town of Malvern at around 9.50pm on Monday.
No property was damaged and no-one was injured in the explosion, police said.
West Mercia Police officers entered a house in nearby Langland Avenue, where they discovered a suspicious substance.
A cordon was put in place and homes evacuated as explosives experts investigated the scene.
The arrested man, from Malvern, was detained on suspicion of possessing an explosive substance, officers added.
Inspector Gareth Lougher said: "We would like to thank people for their patience while we deal with this incident and we would urge people to avoid the area."
Anyone with information is asked to call police on 101 or Crimestoppers anonymously on 0800 555 111.
Police said they did not believe the explosion was linked to terrorism.
In a statement, West Mercia Police said they believed the incident to be "a case of misadventure, albeit with a criminal element".
Superintendent Kevin Purcell said: "At this stage, I am able to confirm that the man arrested and the location are not connected to any terrorism-related matters. The man remains in custody.
"While we are keeping an open mind, one of our lines of inquiry is that this was a case of misadventure, albeit with a criminal element.
"Officers responded promptly to this incident to ensure the safety of local people. Initially we did not know what we were dealing with so we took every necessary precaution."
The police cordon has since been lifted and people allowed to return to their homes.