Disability services in the ACT have been warned to expect a massive spike in demand as the first $10 million of Federal National Disability Insurance Scheme money comes in.

The first tranche of federal cash will begin to flow in July 2013 and will pay for "enhanced disability" services for several thousand Canberrans with a broad range of disabilities including mental illness.

A territory-based program to target funding towards young disabled people aged 18-25 years in Canberra has already begun, according to Disabilities Minister Joy Burch.

In a stopgap measure designed to work until the NDIS begins in earnest in 2014, families are being offered an extra $5000 a year to spend on services for their disabled children who are “transitioning” out of the school-aged care system.

From July, $12 million in federal funding will be available for the ACT's under-prepared disabilities sector to get ready for the extra demand driven by money moving into the sector and for a whole new funding model, away from the traditional "block funding" by government.

But Chief Minister Katy Gallagher confirmed today that the historic scheme will have an "impact" on the territory's budget position in the coming years.

Ms Burch told the Legislative Assembly on Tuesday that she expected about 2500 Canberra users to be accessing the scheme in 2014-2015.

"We expect 2,500 Canberrans with disability and enduring psycho-social disability will begin to receive this support from the NDIS during 2014-2015.

"The number of people supported by the NDIS is likely to increase to approximately 5,000 clients in the NDIS by June 2016.

"In the meantime, from July 2013, the ACT and the Australian Governments will invest $10.6 million dollars to respond to the demand for disability services that we know exists today."