Five people have been pulled from waters south of Adelaide after a boat capsized on Sunday, police say.

The alarm was raised just before 11am, with a Surf Life Saving SA vessel launched for the rescue about 1 kilometre from the shore of Christies Beach.

Police said all boat occupants were brought to shore and taken to hospital.

A SA Health spokesperson said two people were in a critical condition, while the remaining three were stable.

A police helicopter and SA Sea Rescue Squadron also helped in the incident.

Anyone who may have witnessed the incident is asked to call Crime Stoppers on 1800 333 000.

A police officer pulling a tape across a footpath in front of an ambulance and a police vehicle parked on the side street

Emergency services at Christies Beach after a boat carrying five people capsized. (ABC News: Sarah Rohrsheim)