Police are continuing to talk with a 72-year-old man who is believed to be armed with a gun inside a property in Harbour Road, Pagham.
It comes after emergency services were called to the address just after 4pm on Sunday (28 August) to a report of threatening behaviour.
A woman known to the man was also in the house at the time, but she left shortly after police arrival and is safe and well.
The 72-year-old man remains in the property alone.
Detective Superintendent Carwyn Hughes said: "I would like to thank the local community for their patience and understanding while we deal with this ongoing situation.
"Harbour Road remains closed and a cordon around the area is still in place.
"The safety of local residents is our priority and we are doing all we can to make sure their daily routines and Bank Holiday plans are not disrupted. People living in properties along Harbour Road are free to come and go with police support.
"Communication between a trained negotiator and the 72-year-old man in the house continues.”