Denis Napthine has been accused of being "asleep at the wheel" over the future of the car industry, with his South Australian counterpart accusing him of refusing to acknowledge, in private conversations, the looming closures of Holden and Toyota.

In an extraordinary attack, South Australian Premier Jay Weatherill said he repeatedly tried to convince Dr Napthine that Holden and Toyota were on the brink of closing, but his warnings were dismissed as "unlikely".

Victorian Premier Denis Napthine. Credit:Alex Ellinghausen

Mr Weatherill said he had been trying to build a coalition with a fellow automotive manufacturing state in an effort to convince the Abbott government to help the beleaguered industry. He also argued the closure of Holden meant Toyota would follow.

"Poor old Denis has been asleep at the wheel, while we have been out there promoting the interests of the automotive sector in this nation," Mr Weatherill said. "If he did a little a more to get on board a little earlier we might have been able to avoid the decision by the Commonwealth.