Armed police were called to Ditchling Road after 6pm to deal following reports of an armed incident at a property.
Gun shots were reported to have been heard from the site.
Pictures from the scene show a number of Counter Terrorist Specialist Firearms Officers outside a property as well as support from East Sussex Fire and Rescue Service.
Some of the counter terrorism officers were seen with ladders and there have been reports that an armed person was on the roof of a building.
More on this as we have it.