South Yorkshire Police were called at 9.45am today (Saturday 3 May) to reports of an alarm activating at Rotherham Town Hall.
Emergency services attended and a man was found to be in the building.
That man, who is believed to be armed with a hammer, remains in the building and is currently in discussion with specialist trained negotiators.
Nobody else is thought to be in the Town Hall at this time.
A cordon is in place at the scene and The Crofts is closed to traffic while negotiations continue.