DOCTORS made an urgent plea to the Supreme Court yesterday to help save the life of a Jehovah's Witness girl dying of leukaemia.

Justice Richard White ordered the girl, 4, receive treatment, including a blood transfusion to which her parents had objected on religious grounds.

Paediatric oncologist Dr Petra Ritchie, right, said without treatment the girl "will die . . . I would say in weeks".

Dr Ritchie said that the girl, who was diagnosed with cancer of the blood and bone marrow on Monday, had a 90 per cent chance of survival if she received treatment immediately.

Doctors had this week advised she needed a potentially life-saving blood transfusion but her parents objected on religious grounds.

The parents' opposition prompted the hospital to petition the court saying that, without treatment, the girl would die in a matter of weeks.

In emotional scenes yesterday, the girls' father wept as he spoke of his love for his daughter.

But he explained that his family's faith prohibited blood transfusions. "We adhere to strict Bible principles and one of those is to abstain from blood," he said.

"We want the best possible treatment for (her) and the hospital are doing a great job. The only thing we don't consent to is the issue of blood."

The hearing came almost two years after the court made a legal-first ruling to save a boy, 10.

Yesterday Justice White - who also heard the boy's case - said that treatment was in the girl's best interests.

"Without a blood transfusion, there is a very high prospect that (she) will die," he said.

The father told the court that his daughter's illness became known to them about six weeks ago when she reported a sore leg and recorded a temperature.

However, doctors told the family it was a virus and it was not until they took her to hospital on Monday that a diagnosis of leukaemia was formed.

She said the girl was at risk of organ damage to her heart, brain and kidney. Even if the girl survived the leukaemia without a blood transfusion, Dr Ritchie said she could suffer learning difficulties and subtle cognitive and kidney damage.

Todd Golding, for the Woman's and Children's Health Network Inc, said Justice White should interpret the law the way he did in the 2010 case.

"The court is to act in what are the best interests of the child.

"The situation factually, as is clear from the evidence, (the girl) has leukaemia from which she will almost certainly die.

"It is in the submission of the plaintiff that she receive a blood transfusion as soon as possible," he said.

Ken Gluche, for the girl's parents, said his clients "deeply love their child".

"It's not like they are acting with callous disregard for her wellbeing or her future," he said.

"Clearly it's their genuine beliefs, it's something that they've been convinced to accept by anyone else, by the church or other believers."

Robert Croser, for the child, said he had not formally interviewed his client because of her inability to appropriately instruct him. "Nobody on either side of the case wants (the girl) to die," he said.

"Neither (the father) nor his wife and the wider Jehovah's Witness church would treat (the girl) any differently if the court orders she have the blood transfusion."

Justice White handed down his decision immediately.

"I'm satisfied that this is a matter that should be determined urgently because (the girl) suffers from leukaemia and that requires urgent treatment," he said. "I'm satisfied that it is appropriate and indeed necessary for (the girl) to receive a blood transfusion.

"I'm satisfied that there are no alternatives to the provision of a blood transfusion. I'm satisfied that it's in (the girl's) best interest to received the blood transfusion despite her parents' objections.

"Without a blood transfusion there's a very high prospect (the girl) will die and that the provision of a blood transfusion would reduce that prospect markedly," he said.