Seaton, Adelaide: Heartbreaking details emerge about moment five-year-old girl was found limp in the arms of a man screaming for help before she died

South Australian Police are investigating the sudden death of a five-year-old girl at an Adelaide home.

Police Commissioner Grant Stevens said authorities were treating the case 'seriously' and that authorities were trying to establish how the child died on Wednesday.

'It's obviously very tragic when anyone loses their life, more so with a young person,' he told ABC Radio Adelaide.

'Until we have further clarification in relation to the cause and circumstances, we obviously treat it seriously.'

Emergency services were called to a house on Ballater Ave, Seaton in Adelaide's western suburbs about 4pm to reports a five-year-old girl was found unresponsive.

Paramedics treated what authorities believed to be a cardiac arrest incident.

The Major Crimes unit is helping with investigations into her death, which Commissioner Stevens said was the usual for early inquiries due to the child's age.

'When we have a five-year-old child pass away we want to make sure we have the right resources to establish the circumstances as quickly as possible so we can move forward in the right direction,' he said.

Jabar Stanikzai, 13, was walking home from school when he heard a man screaming prompting him to dial triple-zero.

'When I came closer to the man I could see that he was holding a child - a little girl - in his arms and she was limp, not moving or anything and he was yelling her name I think,' he said.

'When he saw me, he shouted at me to call the ambulance so I ran to the phone booth on the street and called the ambulance.'

The five-year-old girl was treated at the scene but later died at the Women's and Children's Hospital.

'The matter is now subject to a coronial investigation. Police will remain at the scene for some time,' a police spokesperson said.

No arrests have been made.