A spokesman for Sussex Police said: "Police officers responded to a report of a man seen with a shotgun in the vicinity of Litten Gardens, Chichester at 2pm on Friday (28 May).
"Officers have now detained a man in relation to the incident.
"As the suspect was reported to be near two schools, we worked with them to take precautions to keep pupils and staff safe while we investigated the report. No threats were made and no one was harmed.
"We would like to thank the public for their patience and understanding while we responded to this fast moving incident."
For rolling updates, see here: Major police incident in Chichester - Live updates