A bomb disposal team from the Royal Logistics Corps is currently at County Hall in Haverfordwest following reports of a 'suspect package'.
A county council spokesman told the Western Telegraph that a partial evacuation had taken place as a result of the alert.
Several police officers and vehicles are parked at County Hall and people are being stopped from entering the premises, including the car park.
A Dyfed-Powys Police spokesman said it was responding to a report of a suspect package in County Hall.
"A partial evacuation has been implemented and officers are preventing any further access to the building as a precaution until Explosives Ordnance Disposal arrive at scene and deal with the package," the spokesman added.