Many residents in Hastings, Bexhill and rural Rother are unable to use the 999 emergency service this afternoon (April 20).
BT has notified emergency services of problems which has led to partial and full disruption of the 999 emergency service. Mobile telephone numbers are not affected.
The telecommunications firm is currently working to restore service to everyone as soon as possible.
The areas currently affected are Baldslow, Bexhill, Hastings, Peasmarsh, Sedlescombe and Wittersham.
People are asked not to make any non-urgent calls for the time being so that all the available phone lines can be used for emergencies.
A Sussex Police spokesperson said: “If you have an emergency, you should first try both landline and mobile telephones to call ‘999’.
“If this does not work, flag down any emergency service vehicle that is not using blue lights or go to the nearest police station, hospital, fire or ambulance station to report the emergency.
“Extra police patrols are out in the affected areas and fire and ambulance resources are being sent to other visible locations.
“Relatives and neighbours of elderly or vulnerable people in the area are asked to check on them more frequently, as their assistance alarms may not operate correctly.
“We will give you an update on the situation as soon as we have more information.”