Debt-ridden GM has taken more than 15 billion dollars in government loans and faces a June 1 deadline to complete a major restructuring plan, failing which it will be forced to follow Chrysler into bankruptcy court.

GM chief executive Fritz Henderson nonetheless remained confident the company could emerge from the flood of red ink. He cited an overhaul plan unveiled last month that would give effective control of GM to the US government and its main union.

Meanwhile German sportscar maker Porsche and giant Volkswagen, the world's second-biggest producer behind Toyota of Japan, on Wednesday unveiled plans for a tie-up, though analysts said the deal still raised a lot of questions.

"It's not really clear how they will construct it," said Juergen Pieper from Metzler Bank.

Following a special meeting of the Porsche family on Wednesday, Porsche and VW gave themselves four weeks to agree on an alliance.

Heavily endebted Porsche would benefit from VW's research and development and access to a vast auto parts purchasing network in addition to VW's hefty cash reserves.