Australia could still miss out on a $A500 million investment by Holden in a V6 engine plant, Victorian Premier Steve Bracks has warned according to a report in the Age newspaper.

Amid speculation that the car manufacturing giant would decide on a location for the new plant this week, Mr Bracks said it was possible the investment could go to North America rather than Victoria or South Australia.

"They have the capacity in the United States to do this sort of facility, so we are not counting any chickens before they have hatched," he told the Age.

The Premier reportedly dismissed claims that Holden would announce its decision this week, possibly as early as tomorrow, saying any announcement was "at least a week off. It (Holden) has some other matters to consider".

Mr Bracks said Victoria had made a "very competitive" offer to attract Holden's investment to the state. It was of "strategic support" rather than money, he said.

"We have a competitive bid in there to operate this in Victoria," he said. "We've got a good skills base, good infrastructure support (and) we are the major car manufacturing production centre in Australia."

Mr Bracks said there was a chance both Victoria and South Australia, who have been competing for the investment for several months, could miss out but he was hopeful.