'Shocked': baby search resumes after tragic discovery

Emergency services are scouring the Port MacDonnell area off the state's Limestone Coast after making a shocking discovery on Monday.

They had earlier been alerted to an abandoned car that was left with its engine running near Cape Northumberland about 11.15am on Monday.

The bodies of a 36-year-old mother and a child aged under three were found in the ocean soon afterwards and retrieved with assistance from local fishermen.

''At this time, there is no information to suggest that any other persons are involved in the incident and reports will be prepared for the coroner,'' police said in a statement on Tuesday.

The woman was from Compton, a small community near Mount Gambier, police said.

SA Premier Peter Malinauskas said there were a lot of unanswered questions, making it very difficult to understand exactly what had transpired.

"These types of tragedies are the ones that shock you to the core," he said on Tuesday.

A number of theories were being investigated but authorities were careful not to jump to conclusions, he said.

"Whenever we see the loss of anybody, it's a tragedy," he said.

"If it involves children, that breaks your heart, particularly when we know there is currently a two-month-old baby that is missing, and that's hard to get your head around.

"I think we can hope and pray for the best in this instance, and that's certainly what we're doing at the moment." 

Detectives and specialist forensic officers travelled to the scene as the search resumed off Cape Northumberland, the state's southernmost point.

Local mayor Kylie Boston said such tragedies were ''always difficult for smaller communities''.

''Everyone's just a little bit shocked at the moment," Southern Limestone Coast Council's Ms Boston told AAP.

"We'll let the police do the work they need to do, and everyone will just continue to support everyone."

She paid tribute to the "fabulous" volunteers amid rough weather that was impacting the search

"I was just at the boat ramp before, it's very windy and quite choppy, which is not helping them," she said.

State Emergency Service duty officer Ian Bonython said responders had encountered ''very dangerous conditions'' on Tuesday.

''There are very rough seas, making it very difficult for marine vessels to get in close to shore,'' he told AAP.

''We have a drone down there, but it's unable to fly because of high winds."

Police held grave fears for the missing baby when the search began on Monday.

"In any conditions, that would cause great concern about the child's ability to survive," Chief Superintendent Trent Cox told reporters.

"We're keeping an open mind about everything, but I don't hold out great hope."

Police are trying to track the women's movements before the tragedy.

Anyone who saw the woman's car, a white 2015 Isuzu MUX with SA Registration S592 BJR, or has any dashcam footage should contact police.

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