Police and emergency services have attended a report of a man with a stab wound to his shoulder in Pavillion Road, Worthing.
It is believed that the man was stabbed at around 2.30pm by another man.
The victim, who is thought to be a man in his 20s, has been flown to the Royal Sussex County Hospital for treatment.
His injuries are not considered life-threatening.
A Sussex Police spokesperson said: “Police are still establishing the circumstances surrounding the incident and we would appeal for anyone who saw the incident to contact police to help us with our enquiries.”
Anyone who witnessed the incident is asked to contact Sussex Police on 101 quoting serial 962 of 1/11 or the independent charity Crimestoppers anonymously on 0800 555 111.