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.