More than three years after revealing plans to cease Australian production, carmaker Holden has confirmed October 20 as its closure date.

The automotive giant said workers at its Elizabeth assembly plant in Adelaide's north were today informed of the deadline.

It said more than 30,000 vehicles would be built before manufacturing ends.

The carmaker said the announcement would provide certainty to its employees as well as the factory's supply chain.

It said nearly 1,000 people remain working at the Elizabeth plant and there were no plans to lay any off before October.

"While this confirmation isn't a surprise for anyone and we've been working toward this for nearly four years, we can now confirm the actual date for our people and our suppliers," Holden's executive director of manufacturing Richard Phillips said in a statement.

"This October may bring to a close more than 60 years of vehicle manufacturing by Holden at Elizabeth but I know it will be business as usual for our manufacturing workforce until then."

Workers relieved to finally have deadline, union says

The Australian Manufacturing Workers' Union said the announcement would provide some much-needed certainty to Holden's employees.

Acting state secretary Colin Fenney said workers who returned from holidays this week had been asking when their last shifts would be, in order to plan their transitions to retirement or other work.

"The people are probably a bit relieved now," he said.

"Now [they] can start looking at what they want to do post-Holden and start working their way towards that."

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Automotive Transformation Minister Kyam Maher said the State Government was offering support to Holden workers through a transition scheme.

"We will certainly continue doing what we've done with the workers," he said.

"We've ramped up only recently our publicity for the scheme to make sure every possible worker is accessing these services."

In December 2013, Holden announced it would stop making vehicles in Australia in 2017 but the exact closure date has, until now, remained unclear.

The decision meant nearly 3,000 people would be out of work, with job losses already having kicked in.

Holden said nearly 700 workers have left the Elizabeth plant since 2015.

"Almost 70 per cent of them have found jobs within 12 months," Mr Maher said.

The flow-on effects on suppliers are predicted to be far greater, with one analyst forecasting about 12,000 job losses as a result of the Holden closure.

The final Holden Cruze rolled off the production line last year.

The State Opposition said it was a "sad day" for workers, and the Government should cut business costs and taxes to generate more jobs.