Parts of Australia's biggest cities could struggle to attract enough disability workers for the National Disability Insurance Scheme (NDIS), a new report has warned.

Key points: Some major cities may not have the capacity to recruit enough staff for NDIS

Some major cities may not have the capacity to recruit enough staff for NDIS Workforce is set to double by 2020

Workforce is set to double by 2020 Service providers have seen demand climb during recent weeks

The Productivity Commission has identified south-west Sydney, southern Melbourne and Logan in Brisbane as areas that currently have less than 40 per cent of the workforce it is expected they will need.

"Some jurisdictions have greater capability to meet workforce targets than others," it said.

"This could suggest that workforce readiness for the full NDIS will be patchy, and that some regions may struggle to be ready even over the long term."

Australia's disability workforce is set to double by 2020 to around 150,000 people.

The commission will examine whether the growth is feasible amid "some evidence that providers are finding it more difficult to recruit staff".

National Disability Services (NDS) chief executive Ken Baker said finding staff can be a challenge.

"Even at this stage, where the demand is not so acute, many disability service providers are having difficulty recruiting staff," Dr Baker said.

"That's not an experience that's evenly distributed around the country, but in some areas it's certainly quite severe."

Dr Baker said money and effort would be needed to recruit staff to certain locations.

"There needs to be a very focused attention to ensure we have the right national workforce strategy to ensure that doesn't become a chronic problem in delivering the NDIS," he said.

The commission said other regions, such as northern Sydney or eastern Adelaide, already had more than 80 per cent of the expected workforce.

NDS is Australia's peak body for non-government disability service organisations.

It surveyed members in 2015 and 2016, finding almost half of all organisations had moderate or extreme difficulty attracting staff.

And it was even harder recruiting for some occupations, such as speech therapists and psychologists.

Demand on the rise

Sydney-based disability service provider Achieve Australia has seen demand climb during recent weeks, forcing it to bolster its 400-strong workforce.

"It was a big spike in new referrals and people coming through," chief executive Anne Bryce said.

"We realised quite quickly that we'd need to think about hiring initially 40 to 50 staff," Ms Bryce said.

"And then subsequently we'll need to hire another 50 to 70 staff, so it's about 25 per cent growth pretty much overnight."

Costs under scrutiny

The Productivity Commission issues paper has been released as part of a scheduled review of the NDIS before it is fully rolled out.

The scheme is expected to cost $22 billion a year and cover 460,000 Australians by the end of the decade.

Cost pressures facing the NDIS will also come under scrutiny.

The commission said more children than expected had joined the scheme, especially in South Australia, Victoria and the ACT.

It also said fewer people than expected had exited the NDIS during trial periods and the cost of care packages was increasing faster than inflation.

The final report is due in September this year.