Premier Jay Weatherill has promised a $35 million investment in faster internet if Labor is re-elected by South Australian voters next month.

He said an existing fibre network would be rebranded as The Fishbone and expanded to be made available to businesses and households across Adelaide.

The infrastructure would be made available to internet providers to offer speeds many times faster than the NBN and would be cheaper, Mr Weatherill said.

"We've already attracted the likes of Boeing and Technicolor to South Australia and this investment in ultra-fast internet will allow us to attract even more exciting businesses."

Mr Weatherill said it would enhance creativity and digital skills in SA.

SA Innovation Minister Kyam Maher said many people had been frustrated by the failings of the NBN.

"We get complaints almost daily from businesses, from households, about NBN — its reliability and its price. It hasn't worked for South Australia. We're stepping in," he said.

NBN 'disaster' for businesses

App and games developer Mighty Kingdom welcomed the plan.

Spokesman Dan Thorsland said good internet was vital for success.

"I need it as much as I need electricity and as much as I need talent. I've got both of those but I don't have fast internet speeds," he said.

"I don't have exactly what I need to get me to the rest of the world.

"For consumers the NBN is a bit of a disappointment but for businesses, it's a disaster. It is not working for what I need."

Adelaide City Council appointed TPG late last year to roll out a fibre-to-premises CBD network, Ten Gigabit Adelaide, starting this year and promising no installation costs for businesses or organisations.

The SA Premier said Adelaide was basing its plan on the experience of the US city of Chattanooga, which has a high-speed city network, and he expected SA would see about 3,000 new jobs across a range of industries.

He said a department of digital innovation was proposed to oversee the expansion of The Fishbone network and look at ways to ensure more people achieved fuller participation in use of the internet.

Business, accommodation plan for old RAH site

Businesses, including start-ups, would benefit from a redevelopment plan for the old Royal Adelaide Hospital site, Labor said as it revealed an office, hotel and short-term accommodation masterplan.

It said $350 million would be committed over nine years, a big part of that in demolition costs and refurbishing heritage buildings on the CBD site vacated by the hospital last September.

Labor wants offices and short-term accommodation on the old Royal Adelaide Hospital site. ( Supplied: SA Labor )

About one-third of the site would be returned to the neighbouring Botanic Gardens under Labor's plan.

Infrastructure Minister Stephen Mullighan said the masterplan "struck the right balance" between private and public needs.

"We think this mix of uses will guarantee both the best return to the state economy by creating new jobs but also provide a great deal more activity for the east end of the city, which will be a great benefit for all of those traders around Rundle Street," he said.

Mr Weatherill announced last year the Government had pulled out of a $1 billion deal for a private consortium to redevelop the site.

Labor has now promised there will not be large-scale apartments on the site.

"There'll be new accommodation for university and research activities, and a limited amount of accommodation for students and visiting researchers and professionals," Mr Mullighan said.

A design competition is also underway for a new contemporary art gallery at the North Terrace site.