Royal Navy bomb disposal experts destroyed a phosphorus flare that was discovered on the Blakeney National Nature Reserve by a warden.
The metal object, which contained a 'nasty substance', was found at 1pm yesterday and the area was immediately cordoned off until it was blown up at 10.15am today (Friday).
A coastguard spokesman said the phosphorus inside the metal casing could cause burning if it came into contact with a person's skin.
She added it would have been used in a recent exercise but it was not clear where it had come from.
No people were harmed and the spokesman said if anyone saw a phosphorus flare, do not touch it and tell the police or coastguard.
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