Bruce Bonyhady, who was instrumental in the scheme's creation, told The Policy Shop podcast that more resources should have been devoted to the challenge for the disability sector, and urged action to address the issue.

Responsibility for managing that adjustment had been blurred between the National Disability Insurance Agency, the federal and state governments, and their departments, he said.

"I think one of the most critical challenges facing the NDIS is how that structural adjustment is facilitated," he said.

"Up to now, it hasn't been a particularly big issue because the growth has been relatively modest, but the real growth is now under way.

"So facilitating that structural adjustment is an essential step and it needs to be done with considerable urgency."

The NDIA said it acknowledged the changes - from direct funding for services to funding allocated to individuals - coming with the scheme presented the disability sector with challenges, and said it was working with state and federal governments to deliver the reform.

"A core driver of this transformation will be that participants and people living with disability will increasingly become informed consumers and will therefore shape the type and nature of supports that are offered in the sector," it said.

Australian Federation of Disability Organisations chief executive Ross Joyce said the previous system was patchy, difficult to navigate and provided supports that varied depending upon location, and the NDIS had been a welcome improvement.

There had been confusion across some states and territories about the need to continue providing supports and services for people with disability, having signed off on the introduction of the NDIS, he said.

"This is not only until the scheme is fully rolled out but also in an ongoing setting for the disability sector," Mr Joyce said.

"There have been some governments at this level that have been prematurely withdrawing or discontinuing services or supports in the mistaken belief that the NDIS will take over all of the needs in the sector."

The Turnbull government in October rejected a call to delay the full roll-out of the $22 billion NDIS, despite a major report finding the current timetable was compromising the quality of care and threatened the scheme's financial viability.

The Productivity Commission found the current timetable simply "will not be met" as the scheme struggled under a "tsunami" of demand.

In its report to the government after a year-long inquiry, the commission said federal and state governments must start planning to delay the start of the full scheme beyond 2019-20.

It also warned of acute skills shortages and other price pressures that could force up the cost of the scheme, described as the biggest social reform in Australia since the introduction of Medicare.

The commission also said the NDIS - currently in a transitional phase as it ramps up towards full launch - was already improving the lives of many participants, their families and carers.

Dr Bonyhady, considered the father of the NDIS, has been vocal about the scheme's future previously, arguing for his board's independence before he left the chairman's role.

Listen to the full interview by The Policy Shop here.