Bournemouth beach was evacuated as rescuers pulled at least two people from the sea and airlifted them to hospital.
Coastguard resp pulled from the waves at least two young people who had reportedly been dragged out to sea.
Hundreds of sunbathers enjoying the warm weather were asked to leave the beach on Wednesday afternoon to allow air ambulances to land.
The South West Ambulance Service said two people were taken to hospital. Their condition has not been made public.
One witness told ITV Meridian that they saw three people – possibly teenagers – being rescued from the water.
Emergency services were called just after 4.30pm, including South West Ambulance Service, two air ambulances, Poole and Southbourne coastguard rescue teams, an RNLI lifeboat and Dorset Police.
The ambulance trust said it sent two air ambulances, six double-crewed land ambulances, a critical care car, two operations officers, a doctor, a hazardous area response team and a responding officer.
“We conveyed two patients to Royal Bournemouth Hospital and Poole Hospital,” it added.
A police cordon was put in place around the area and a nearby flyover was closed to traffic.
A spokesman for Dorset Police said the force received a report at 4.32pm from the ambulance service requesting assistance on the beach off Bournemouth Pier.
“Officers are currently in attendance clearing the area to assist HM Coastguard and the ambulance service, who are dealing with the incident,” they added.
Several witnesses said on social media they saw two air ambulances overhead, as well as police jet skis searching the water.
Groups of emergency service workers gathered on the beach, and there were unconfirmed reports that CPR was being carried out by professionals.
A coastguard spokesman’s statement read: “Two people had been pulled from the water and passed into the care of the ambulance service. Coastguards searched to make sure there were no other people missing, and are satisfied there are not.”
University Hospitals Dorset NHS Foundation Trust says it was “working on a response” to what happened.