Sussex Police said the incident took place in Warrior Square.
A spokesperson said: “Police assisted emergency services following a report of a man falling from height in Warrior Square, St Leonards at around 8.55am on Wednesday, July 17.
“A man was taken to hospital with serious injuries.
“The Health and Safety Executive have been informed.”
The air ambulance was also called to the scene, as well as the fire service.
A spokesperson for East Sussex Fire and Rescue Service (ESFRS) said: “We were called on July 17 at 8.48am to reports of a rescue from height in Warrior Square, St Leonards.
“Crews from Bohemia Road Hastings, The Ridge Hastings, Battle and Bexhill, including the Aerial Ladder Platform and rope rescue team, assisted emergency services to rescue the casualty who was handed over to the care of the Ambulance Service.
“Sussex Police, South East Coast Ambulance Service and Helicopter Emergency Medical Service (HEMS) were also in attendance.”
A spokesperson for SECAmb said: “We were called shortly after 8.30am to reports a person had suffered a fall from height in Warrior Square, St Leonards.
“Ambulance crews attended and were joined at the scene by the Air Ambulance Charity Kent, Surrey, Sussex. The person was assessed and treated at the scene before being airlifted to Royal Sussex County Hospital in Brighton.”
“A man was taken to hospital with serious injuries.