GM Chairman Ed Whitacre announced Henderson's surprise resignation at a hastily convened press conference in Detroit, following a meeting of the 13-member board.

"While momentum has been building over the past several months, all involved agree that changes needed to be made," Whitacre said, declining to give any details as to why Henderson was leaving.

Whitacre will assume the post of interim CEO until a replacement for Henderson is found.

The 51-year-old Henderson replaced Rick Wagoner in March at the helm of GM, after the US government became chief shareholder as part of a bailout for the struggling automaker.

The US government said on Tuesday that it was "not involved in the decision."

Whitacre and Henderson had disagreed over whether to seek financial aid from the German government to save its European subsidiary Opel.

Henderson had brokered an all-but-done-deal to sell off Opel to Canadian car parts manufacturer Magna and Russia's Sberbank.

But the GM board, under Whitacre, scuppered Henderson's plan and instead decided to restructure the Opel unit itself.

The surprise move sparked outrage in Germany, which was prepared to back the Magna deal with billions of euros of state aid.

Opel employs 50,000 people in Europe. GM has said it intends to reduce costs by 30 per cent, including the elimination of around 10,000 jobs.

nk/dpa/AP/AFP/Reuters
Editor: Chuck Penfold