Two people are believed to have died following an explosion on an industrial estate.
Police, paramedics and firefighters were called to digger bucket manufacturer Harford Attachments in Spar Road, Hellesdon, Norwich, at 9.20am.
Norfolk Police said there were a "number of casualties". These are understood to include two fatalities although the force is yet to confirm this.
A helicopter from the East Anglian Air Ambulance was also deployed, although this crew did not include the Duke of Cambridge, who began work with the charity today.
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The estate has largely been shut off to the public.