Police are at the scene of an incident at John Street in Derry where they say they have concerns for the safety of a man.
The alert was raised at about 2.30pm. Officers have spoken to the man, who is in a block of flats overlooking the street.
Police say the situation at the moment has been contained and they do not believe there is any direct threat to other members of the public.
John Street and a stretch of road adjacent to the Foyle Road car park have been closed to traffic and pedestrians.