Emergency services praised the efforts of bystanders who rushed to the aid of an unconscious and unresponsive toddler who fell and hit his head at Clontarf Beach beside Sydney Harbour today.

The quick application of CPR by the bystanders, including an off-duty nurse, brought the toddler back to effective breathing when emergency services reached the secluded beach shortly after 10.30am.

It was initially feared the boy may have been pulled unconscious from the water.

CareFlight landed at the park to allow the crew trauma doctor to join ambulance paramedics and police who had rushed to the beach.

The CareFlight doctor said the 16-month-old toddler, from Newport, was having fun at the beach on an outing with his grandmother when he fell and struck his head.

The doctor and paramedics continued treating the boy as he was taken in a road ambulance to Royal North Shore Hospital, for observation, where he remained in stable condition on arrival.

The doctor said it was important for any child to be expertly monitored in hospital after suffering decreased consciousness from a blow to the head, to ensure there was no subsequent underlying damage to the brain.