Police were called shortly after 3pm to reports of a man with a gun.
Armed police and paramedics attended the scene for more than two hours.
At 5.30pm, a man was led out in handcuffs and the roads began to reopen.
A 34-year-old man is being questioned by Sussex Police officers on suspicion of commiting an offence under the Firearms Act. Officers are searching a house this evening.
No shots were fired and nobody was injured in the incident.
Detective Superintendent Steve Black, who led the operation, said: "I would like to thank everyone for their patience and co-operation while this sensitive incident was brought to a safe conclusion.
"I am aware that there was significant disruption, but it was essential to close off the immediate area to ensure the safety of everyone living and working locally, as well as those seeking to resolve it."
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