Both Hornsea and Bridlington Coastguard teams were called out and the Yorkshire Air Ambulance landed as several of the casualties had been injured when they were swept against a groyne, one of the beach's anti-erosion defences.
The number of rescued swimmers is thought to have been six, but their ages or the extent of their injuries have not been given.
The conditions in the sea off Hornsea on Thursday were described as 'rough' despite the warm and dry weather.
Hornsea Coastguard said: "We were tasked along with Bridlington Coastguard Rescue Team to a report of multiple persons in difficulty on Hornsea South Beach with a number of casualties unaccounted for.
"When teams arrived on scene a number of casualties were already being treated by Hornsea Inshore Rescue crew, Yorkshire Ambulance Service, and the Yorkshire Air Ambulance had landed to provide advanced medical care.
"The incident had occurred when a number of persons had been swimming in a rough sea and got into difficulty, they had sustained injuries after being swept into a groyne and struggled to swim in the rough swell.
"Coastguards assisted with securing the helicopter landing site and managed a safe cordon ready for the air ambulance to depart. All casualties were left in the care of ambulance staff.
"If you see anyone get into difficulty at the coast always dial 999 immediately and ask for the Coastguard. Where possible swim at a lifeguard manned beach and seek advice from lifeguards on safe swimming conditions.
"RNLI lifeguards Yorkshire are now in Hornsea throughout the summer season, it is advisable to swim when RNLI lifeguards are on duty and to swim in the designated area near the central promenade by the leisure centre where they are located."
The volunteer-run Hornsea Inshore Rescue organisation added: "Team called out today to multiple swimmers that had been injured whilst attempting to swim in rough sea conditions.
"First aid administered by the lifeboat team and handed over to the ambulance team and Yorkshire Air Ambulance .
"Please ensure if wanting to enter the sea that conditions are suitable and where possible swim where the lifeguards are located."