A six-month-old girl has suffered from life-threatening seizures after her mother fed her cordial because she could not afford to buy her infant formula.

Doctors and breastfeeding advocates say the incident, detailed in a medical journal, shows the danger of mothers being pushed into using formula too early with little understanding of the potential risks.

The little girl was brought to a hospital in Coffs Harbour after she started experiencing the seizures.

Her mother told doctors she had replaced the formula with green cordial for some of her feeds when the formula had become too expensive. The little girl had been fed formula since she was five weeks old.

Paediatric registrar Rakel Hansen said this was the first such case recorded in Australia, although it happened more commonly in the United States.