Officers were originally called to Bunn Leisure Caravan Park in Warner Lane yesterday evening after receiving reports of an altercation between two people. A 29-year-old Southampton woman was arrested on suspicion of assault.
The incident took a more serious turn when later that evening when a man made threats to harm himself and police officers at the scene, police have said.
Armed police and negotiators were called and a 29-year-old man, also from Southampton, was arrested on suspicion of making threats to kill.
The pair remain in custody as police continue to investigate the incident.
Bunn Leisure confirmed there had been a 'domestic incident' at the site.
A spokesman for Sussex Police has said: "Police were called to a caravan park in Warner’s Lane, Selsey over reports of an altercation between two people at 6.42pm on Wednesday (September 8).
"A woman aged 29 from Southampton was arrested on suspicion of assault.
"Later, officers from the Tactical Firearms Unit (TFU) were called to the site after a man made threats to harm himself and officers present.
"Negotiators engaged with the man, aged 29 and also from Southampton, and he was safely detained by officers. He was arrested on suspicion of making threats to kill.
"Officers are continuing to investigate this incident and both suspects remain in police custody."