Sussex Police said officers attended an address in Lindum Road shortly after 6pm 'to arrest a wanted individual'.
"The road was closed in both directions for approximately 30 minutes," a police spokesman said.
"A 22-year-old man from Worthing was arrested on suspicion of harassment and possession of a firearm."
Police said on Monday morning (June 13) that the suspect remained in custody.
The spokesperson added: "The incident was not related to counter terrorism."
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Armed police in Lindum Road, Worthing. Photo: Eddie Mitchell
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Armed police in Lindum Road, Worthing. Photo: Eddie Mitchell
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Armed police in Lindum Road, Worthing. Photo: Eddie Mitchell
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Armed police in Lindum Road, Worthing. Photo: Eddie Mitchell