Nine people are awaiting treatment after a suspected chemical leak which forced the evacuation of a council office for the second time in less than a fortnight.
The Essex County Council building in The Crescent, Colchester, was first cleared by authorities on June 29 after reports of people falling unwell and reporting a strange smell.
Essex County Fire and Rescue Service said a similar incident had taken place this morning.
A spokesman for the force said: "The building has now been fully evacuated and all people have been accounted for.
"Nine people are awaiting triage from the ambulance service. They are all receiving oxygen therapy from firefighters."
A specialist Detection Identification and Monitoring (Dim) vehicle from Epping - on its first emergency incident - has been sent to the scene to assist in identifying the chemical involved.
Ambulance crews, specialist officers and the trusts hazardous area response team (Hart) were sent to the council office to deal with the incident after being alerted to a report of several people taken unwell at 10.40am, the East of England Ambulance Service said.
Ambulance service spokesman Gary Sanderson said: "At present our team of ambulance crews are working closely with the fire service to ascertain what has caused the sudden illness of the members of public at this location this morning."