Rescuers searching for a man lost in waters off the South Australian coast for 20 hours say they aren’t giving up hope of finding him alive.

Just after 4pm on Friday, police and emergency services were called to Mary Ellis Beach, southwest of Port Lincoln, amid reports of people caught in a rip and unable to return to shore.

Six people were helped from the water and treated at the scene, with four children taken to hospital.

A 43-year-old Roxby Downs man who was with the group remains missing.

SA Police Superintendent Paul Bahr said conditions at the time were windy with “quite high” waves “dumping severely”.

“It was difficult conditions for swimmers,” he said.

“At this stage, the weather conditions are warm, the sea temperature is warm and we are not giving up hope just yet.”

He said visitors to the region needed to be aware that waters off the coastline were part the Southern Ocean and subject to everything that comes with an ocean.

The search resumed on Saturday before 7am, with police helicopters, SES drones, a boat and ground crews taking part.

-AAP