South Australia's unemployment rate has settled below 6 per cent for the first time in four years, a day ahead of the loss of nearly 1,000 Holden jobs in Adelaide's north.

Australian Bureau of Statistics figures show that the headline seasonally adjusted rate rose from 5.8 to 5.9 per cent in September, but the less volatile trend figure fell from 6 to 5.8 per cent.

The last time both measures were below 6 per cent was in March 2013.

The unemployment rate in SA remains above the national average of 5.5 per cent.

But the state now sits amid the pack on unemployment figures, with a lower trend rate than Victoria, Queensland and Tasmania, but a higher rate than New South Wales and Western Australia.

"I welcome the figures, but with the closure of Holden tomorrow we cannot be complacent," SA Employment Minister Kyam Maher said.

Holden's Elizabeth plant is set to close its doors for the last time on Friday, ending the jobs of up to 950 people.

Its closure will signify the end of vehicle manufacturing in Australia following the exit of Toyota earlier this month, Ford last year, and Mitsubishi in 2008.

Opposition industry spokesperson Corey Wingard said the number of full-time jobs fell in SA last month and "many more" would be at risk when Holden closed.

"Indeed, there are 10,200 fewer full-time jobs today than there were in February 2010 when [former premier] Mike Rann promised to create 100,000 extra jobs," he said.

"The youth unemployment rate here in SA is the second highest in the nation."

He said the Liberals welcomed the drop in the unemployment rate on trend terms but remained concerned ahead of Holden's closure.

But the Government said there had been strong investment across SA, including the sale of steelmaker Arrium to the GFC Alliance, $900 million invested into the Carrapateena copper mine by OZ Minerals, and Solar Reserve's $650 million solar thermal investment at Port Augusta.

"Today's unemployment figures show that there has now been two years of consecutive monthly jobs growth, with a record 828,100 people in work," Mr Maher said.

"The state's unemployment figure is now 1 per cent less than the exact same time as last year, down from 6.8 per cent to 5.8 per cent.

Premier Jay Weatherill said South Australia was now in a much better position to be able to "absorb" the Holden job cuts.

"We're now off the bottom of the pack in terms of unemployment," he said.

"We're now very much in the middle of the pack, which is an extraordinary achievement given that half of Holden has already closed and many of the component manufacturers have also been shedding jobs here.

"We've created jobs in the South Australian economy so we can more effectively absorb the shock that's about to come to us."

$300m bus project could create jobs for ex-Holden workers

The Government also revealed that former Holden workers could soon be building buses for Adelaide's public transport network.

On Thursday it announced a $300-million tender to provide 400 new buses over the next 10 years, about 40 per cent of the Adelaide Metro network.

Mr Weatherill said the tender would give double the usual weighting for local industry and local jobs.

"This tender gives us the opportunity to construct it in a way which will create jobs here in South Australia," he said.

"We've got some fantastic local builders that were formerly part of the component manufacturers industry and they'll have an opportunity to bid into this particular tender process."

Transport Minister Stephen Mullighan said a long-term contract would provide enough certainty for local bus manufacturers to invest.

"We lost Custom Coaches here in 2014 merely because they weren't getting the volumes across Australia to keep open so many manufacturing sites," he said.

"But going out with this many buses gives the best opportunity for either bus manufacturing to occur here or at least for component manufacturing to occur here."