Police are urging anyone with mobile phone or CCTV footage of the stabbing in Littlehampton to come forward.
Officers attended Terminus Road in the town centre at around 2.45pm yesterday and discovered the three victims in the nearby High Street.
A 17-year-old boy and a 16-year-old boy suffered serious injuries from being stabbed. Both remain in a stable condition at the Royal Sussex County Hospital, Brighton.
A third victim, a 16-year-old boy, suffered minor injuries as part of the same incident.
The suspect, a 16-year-old boy from Worthing, was arrested on suspicion of grievous bodily harm with intent and remains in custody.
The four teenagers involved are believed to be known to each other and police are continuing with enquiries this morning.
Sussex Police are carrying out increased patrols while the investigation continues.
Anyone who witnessed the incident or has any footage please report online or call 101 quoting reference Operation Sudbury. Alternatively, you can visit the Crimestoppers website or contact the independent charity anonymously on 0800 555 111.
Bystanders caught up in the incident described the attack as ‘terrifying’. Click here to read more eyewitness accounts.