About 600 Bridgestone employees have been told the company's tyre-making plant at Salisbury in Adelaide will be closing within six months.

The company says international competition is behind its decision, not the global financial crisis.

Senior executive director Andrew Moffatt says Bridgestone has been reviewing its operations for many years and the Salisbury plant's operations are no longer viable.

"We've been working with the employees and the management and we've made significant investment in these factories over a number of years to improve their cost competitiveness, to improve the fact that those factories can survive in the long term," he said.

"Unfortunately we've not succeeded in this."

Employee Darren Iron was told of the closure this afternoon.

"The actual managers told us to go home and we'll be paid what we should be for the rest of this day," he said.

South Australian Premier Mike Rann says he is disappointed that the decision was made by management in Japan.

In 2007, Bridgestone became a private company, wholly owned by its Japanese parent.

Mr Rann says he was only told about the closure by a staff member at 1:00pm today.

"It's a similar thing to what happened to Mitsubishi," he said.

"Here we've got companies that in my view were less than frank with people. The bottom line for me is helping these workers."

The Opposition's employment participation spokesman, Andrew Southcott, says it is a blow for the region.

"These jobs are located in northern Adelaide, which is already an area of high unemployment, it's already an area of social disadvantage," he said.

"That's why it's important that both the South Australian and Federal Government look at providing a structural adjustment package."

Union shocked

The company says all employees will receive their full entitlements.

South Australia's secretary at the Australian Manufacturing Workers Union, John Camillo, says Brigestone's announcement came without warning.

"It is a sudden shock, we knew they were doing it tough over the last few years but my concern now is there's no way we can save the company," he said.

"But [we need to] seriously sit down with the company, with the state and federal governments, to look at training these people."

Mr Camillo says it has been difficult for union members to swallow the company's decision.

"My main focus now is to see what we can do for these people, told now, who will go home and talk to their families about not having full-time employment and what they need to do to continue," he said.

"While there is a redundancy package already negotiated, we just have to be mindful that these people find employment elsewhere."

A plant in Christchurch in New Zealand which employs about 275 workers will also close at the end of this year.

Bridgestone says more than 1,500 other employees working in its distribution, customer service and retail networks will not be affected by the closures.