Firefighters were called to a suspected chemical incident at an industrial estate in Thetford last night.
Crews from King's Lynn and Norwich were dispatched to the area, along with local units, shortly before 10pm.
In all two appliances from Thetford, one from Kings Lynn South and the Environmental protection unit from Sprowston attended to reports of a chemical incident on Brunel Way. Crews used gas monitoring equipment to make sure the scene was safe.
Three people were exposed to potentially toxic fumes. Officers from Norfolk Police said they were called due to concerns for safety of occupants of the unit.
A spokesman said: 'They believe the chemicals have been mixed incorrectly causing some fumes at a premises on Brunel Way.
'Three people were exposed to these fumes in total. We were told as a precaution in terms of evacuation.'
Norfolk Fire and Rescue cordoned off the affected area and evacuated people from within the unit.
A spokesman for the ambulance service said: 'We were called at 9.55pm yesterday with reports of potentially harmful chemical fumes in Brunel Way, Thetford.
'We sent the Hazardous Area Response Team (HART) and an ambulance officer. several patients declined medical treatment and no-one required transport to hospital.'
Emergency services left at just before midnight.
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