A keeper at one of Sydney's premier zoos has been left critically injured after an elephant calf crushed her against a fence post.

The woman, named in Australian media reports as senior elephant keeper Lucy Melo, was washing the 2-year-old male Asian elephant in a barn at Taronga Zoo when the accident happened on Friday.

Andrew Wood from New South Wales Ambulance Service said: "When ambulance crews arrived, the patient was conscious and talking."

"She did briefly say what has happened. The patient then went into cardiac arrest."

It is believed the elephant involved is named Mr. Shuffles and became known as the "miracle elephant" when he was born, after vets thought he had died in the womb.

Taronga Zoo's Chief Executive, Cameron Kerr, said: "It is surprising and we'll be reviewing the situation very carefully."

In the an update from the zoo on Friday evening they said an investigation was underway and the keeper was still in a critical but stable condition.