NDIS demand won't affect services: Fifield

The federal government says no national disability insurance scheme clients in South Australia will miss out despite double the expected number of people applying for services.

However, federal Disabilities Minister Mitch Fifield said there would be delays in processing due to the high demand.

Around 10,000 children have been identified as eligible for the child-focused trial scheme in SA - twice as many as originally expected.

Senator Fifield said officials were working with the SA government to find a solution to what was a "fundamental error in numbers" agreed by the Gillard and Weatherill governments.

"The commonwealth has committed to bearing 100 per cent of the risk of higher than expected costs during the trial, and there is no change to that arrangement," the minister told AAP on Monday.

"No one will miss out on services."

While there were delays in moving over to the NDIS, anyone currently receiving state or commonwealth support would continue to receive it until they are transitioned into the scheme.

Anyone not support in existing systems will be fast-tracked through the NDIS, the minister said.