The mother of the four-day-old baby boy had had hepatitis 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 (DOCS) took out a Supreme Court order to force the parents to immunise their child, but has so far been unable to locate the couple.

A spokeswoman said the department would have to go back to court Tuesday if the parents were not found.

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.

The baby's father, a financial adviser, is seeking an injunction against the court order, and is adamant the family will stay on the run indefinitely.

The couple, from Croydon Park, fled their home on Thursday to avoid police and DoCS officers, after refusing to have their newborn son vaccinated at Sydney's Royal Prince Alfred Hospital.

They fear that aluminum in the vaccine could cause their child neurological damage and are confident that the hepatitis virus can be managed effectively without vaccination.