More than 10,000 people with a disability and 6000 workers face an uncertain future as the NSW government moves ahead with plans to transfer services to the private sector ahead of the introduction of the National Disability Insurance Scheme.

Disability advocates have raised concerns about continuity of care, and the union representing workers has warned many will leave the sector under the transfer of Ageing, Disability and Home Care (ADHC) services to non-government organisations.

Non-government service providers have welcomed the move, saying it would lead to greater choice for people with disabilities.

They will be asked to lodge expressions of interest in taking over almost 400 state-run specialist disability services worth $550 million, with the process to start on May 16.

Executive director of the NSW Council for Intellectual Disability Aine Healy said she was relieved to see more details about the transfer, which was announced in 2014.

"This has been a very stressful time for people with disability and their families," she said.

She called for a guarantee that services for some of the state's most vulnerable people would be maintained.

"This is a particular concern for people with complex needs and there needs to be assurance that their needs will be met," she said.

Steve Turner, assistant general secretary of the Public Service Association, which represents many ADHC workers, questioned whether non-government providers could cover the 40 per cent of services such as group homes, clinical care and respite programs now provided by the state.

"There is no provider of last resort under this transfer so we are deeply concerned about what that will mean for people with more complex needs," he said.

He warned the transfer would force skilled staff out of the sector, although an analysis by the National Disability Insurance Agency forecasts increased demand for workers as the NDIS rolls out from July 1.

Tony Pooley, National Disability Services state operations manager, said non-government groups would welcome ADHC staff in helping to ensure a seamless transition.

"It's not in the government's interest, it's not in the service provider's interest and, most importantly, it's not in the interests of the person receiving the service, to have any uncertainty about the process," he said. "Clients will not be left in the lurch."

NSW Disability Minister John Ajaka said offering state-run services to new providers would result in greater choice.

"The NSW government's main priority during this transfer is the continuity of top-quality care for people with disability," he said. "I will continue to ensure their views inform this process."

Opposition disability spokeswoman Sophie Cotsis recommended independent scrutiny of the transfer.

"The Baird government must outline what protections it will put in place to ensure that there is independent oversight of this process so that people with disability do not fall between the cracks," she said.