Police continue to have a large presence in Crawley following the incident at Crawley College.
A spokesman said: “Officers received multiple calls shortly after 3.10pm on Monday (26 April) to reports of gun shots being fired at a college in College Road, Crawley.
“Armed police were swiftly on scene and an 18-year-old man from Crawley was detained in College Road at 3.20pm and remains in custody at this time. A firearm and a knife were seized.”
Two college staff members were treated for minor injuries, said police. These were not gunshot wounds.
Pupils and staff were evacuated to a safe space while police carried out a search of the buildings.
Chief Superintendent Howard Hodges added: “We continue to have a large policing presence in Crawley and are appealing for anyone with information to come forward.
“Two staff members at the College suffered minor injuries and presented themselves to a walk-in medical centre. No one else has presented themselves to use with injuries but if you need medical assistance please contact the ambulance service or speak to an officer.
“We are liaising with officers at Counter Terrorism Policing South East (CTPSE). All lines of enquiry are open at this stage.
“Roads in the vicinity of the college have been closed and we continue to ask members of the public to stay away from the area at this time.”
The spokesman said: “Report information by calling 101 or report online quoting Operation Reset.”