Police were called to George Street at 6.10pm yesterday (Monday, May 3) after a report that a man in his 30s had been assaulted.
He was taken to the Royal Sussex County Hospital in Brighton for treatment to a single stab wound and is now in a stable condition.
After carrying out fast-time enquiries, police arrested three boys on suspicion of wounding with intent and two boys on suspicion of grievous bodily harm with intent.
They all remain in custody at this time.
Inspector Aidan Cornwall, of the Hastings Neighbourhood Policing Team, said: “We understand this incident may have caused concern and we would like to reassure the public that we are thoroughly investigating the matter.
“We will not tolerate violence in our communities and we are committed to reducing knife crime and knife possession, and taking harmful items off our streets.
“This is being treated as an isolated incident and we continue to appeal for anyone who saw what happened to please get in touch to assist with our enquiries.”
Investigating officers are keen to speak to anyone who saw what happened, or who may have any other information. Police can be contacted online or by calling 101 quoting Operation Mast.
Alternatively, they can contact the independent charity Crimestoppers anonymously online or by calling 0800 555 111.