Authorities are still searching for a Sydney couple who are in hiding after refusing to have their newborn baby vaccinated against hepatitis B.

The mother of the four-day-old baby boy has had the virus for several years and doctors say the child runs a high risk of contracting it unless he is immunised within days.

The New South Wales Department of Community Services has taken out a Supreme Court order to force the parents to immunise their child, but has so far been unable to locate the couple.

A DOCs spokeswoman says the department will have to go back to court tomorrow if the parents are not found.

The parents, who are from Croydon Park in western Sydney, believe the illness can be managed more effectively than any potential damage from the vaccine.

The couple believes aluminium in the vaccine could cause the baby more damage than contracting hepatitis B.

The parents have the support of the anti-vaccination group the Australian Vaccination Network.

The baby's father, who is seeking an injunction against the court order, was adamant the family would stay on the run indefinitely.

One of the doctors who alerted state authorities to the couple's refusal to have the baby vaccinated, Professor David Isaacs from Sydney's Westmead Children's Hospital, said yesterday that the child's rights were being ignored.

"If you do not immunise a baby in this situation, you're putting that baby's life at risk," he said.

He said if a baby gets hepatitis B at birth he or she will become a chronic carrier of the virus.

"About a third of those chronic carriers will die young from cancer of the liver or cirrhosis of the liver ... this is a horrible disease," he said.

While vaccinations are not compulsory in Australia, New South Wales state health policy mandates that parents of all babies born to hepatitis B-positive mothers must be offered immunoglobulin for the child within 12 hours of birth and four doses of the vaccine over six months.

New South Wales Assistant Police Commissioner Frank Mennilli yesterday declined to say whether the parents would be charged once they were found.

"It'll be something that'll have to be assessed once that child is located," he said.