A number of people are said to have been injured following a suspected explosion at an industrial estate in Norfolk.
Police said they are dealing with an "industrial incident" at the estate in Spar Road, Hellesdon, in Norwich.
There are believed to be a number of casualties although the severity of their injuries is unconfirmed.
Firefighters from Norfolk Fire and Rescue Service and the Air Ambulance Service are also at the scene of what appears to be an explosion at one of the factories on the site.
Keith Swann, 56, branch manager of nearby Automotive Parts Distribution, told the Eastern Daily Press: "There was a big cloud of black smoke behind us. We could see the black smoke coming across the top of the building and it went really dark. We didn't know what was going on. Ten minutes after that, the air ambulance arrived."
A Norfolk police spokesperson said: "Officers from Norfolk Constabulary are currently at the scene of an ongoing industrial incident in Hellesdon.
"It is thought to have taken place at 9.20am this morning [Monday 13 July 2015] at an industrial premises on Spar Road. There are believed to be a number of casualties although the severity of their injuries has not been confirmed at this time.
"All emergency services are at the scene while road closures and exclusion zones are currently being considered."