The National Disability Insurance Scheme's latest site in Sydney's west has been swamped with demand from children with disabilities, with more than twice as many applications than expected.
The National Disability Insurance Agency, which administers the scheme, estimated 167 young people would apply for support in the first month of the Nepean Blue Mountains program, which started in July.
Figures from the agency show almost 400 applicants were deemed eligible in the first month of the scheme, which is initially being offered to children and young people under 18.
The NDIA's quarterly report on sustainability of the scheme, released on Thursday, shows the biggest demand is among participants on support packages worth $10,000-$30,000 per year.
The report found only 30 per cent of plans expected to be approved had been completed for participants in the Nepean and Blue Mountains region, putting the site behind the national average of 73 per cent.
According to the NDIA, the majority of participants in the Nepean and Blue Mountains site are aged between 5-14 and almost two-thirds of them cited autism and related disorders as their primary disability.
Tamara Van Antwerpen, general manager of the the Luke Priddis Foundation, a Penrith-based autism spectrum disorders support organisation, said families were crying out for support.
"That number is just a drop in the ocean compared with what's coming," she said. "There are many more people currently filling out their application forms who will more than likely be eligible."
She said pent-up demand for autism therapy was driven by a gap in previous funding policy.
"Previously funding would cut out when the child turned seven but there is a large number of children aged over seven who need support but their families are unable to afford it," she said. "That's where a lot of the demand for NDIS packages is coming from."
A spokeswoman for the NDIA said the agency had not underestimated demand.
"There are not more participants than expected, simply a large number of participants seeking access to the scheme in the first few weeks following its launch in the Nepean Blue Mountains," she said.
The NDIA estimates almost 2000 children with a disability in the Nepean and Blue Mountains site will gradually phase into the scheme which the spokeswoman said was running "on time and on budget".
NSW minister for disability John Ajaka said funded early intervention services for children would have, "long term positive outcomes."
About 460,000 Australians will receive support when the $22 billion scheme is fully operational in 2018.